Having problems with SImulink

This model worked fine before today. I now get the following error (below). I have searched for it online and followed people's suggestions, but the problem is still there and I have no idea how to fix it.

failed assertion in b:\matlab\toolbox\stateflow\src\stateflow\utils\object.cpp at line 2312:

object[id] != nullptr

[ 0] 0x00000002b4ee4567 bin\win64\stateflow.dll+04932967 SF::SD::setSymbolicSizeOnData+00423543

[ 1] 0x00000002b5eb345e bin\win64\stateflow.dll+21509214 SF::mx2str_write_str+00037422

[ 2] 0x00000002b5961b8d bin\win64\stateflow.dll+15932301 SF::sf_mexFunction+00002861

[ 3] 0x00000002b5961075 bin\win64\stateflow.dll+15929461 SF::sf_mexFunction+00000021

[ 4] 0x00000000fc634844 bin\win64\libmex.dll+00346180 MexRetrieveVersion+00003348

[ 5] 0x00000000fc634ba4 bin\win64\libmex.dll+00347044 MexRetrieveVersion+00004212

[ 6] 0x00000000fc618089 bin\win64\libmex.dll+00229513 mexUnlock+00024825

[ 7] 0x00000000175e9a66 bin\win64\pgo\m_dispatcher.dll+00039526 Mfh_file::dispatch_file_common+00000210

[ 8] 0x000000001767252e bin\win64\pgo\m_dispatcher.dll+00599342 Mfh_error::lookup+00005234

[ 9] 0x0000000017672dcd bin\win64\pgo\m_dispatcher.dll+00601549 Mfh_file::dispatch+00000045

[ 10] 0x00000000184731d9 bin\win64\pgo\m_lxe.dll+00274905

[ 11] 0x0000000018631ba2 bin\win64\pgo\m_lxe.dll+02104226 mwboost::archive::detail::oserializer<mwboost::archive::binary_oarchive,foundation::msg_svc::eventmgr::BaseEvent>::oserializer<mwboost::archive::binary_oarchive,foundation::msg_svc::eventmgr::BaseEvent>+00073902

[ 12] 0x00000000184793e1 bin\win64\pgo\m_lxe.dll+00300001

[ 13] 0x000000001863be3d bin\win64\pgo\m_lxe.dll+02145853 mwboost::archive::detail::oserializer<mwboost::archive::binary_oarchive,foundation::msg_svc::eventmgr::BaseEvent>::oserializer<mwboost::archive::binary_oarchive,foundation::msg_svc::eventmgr::BaseEvent>+00115529

[ 14] 0x0000000018478bd6 bin\win64\pgo\m_lxe.dll+00297942

[ 15] 0x0000000018476f03 bin\win64\pgo\m_lxe.dll+00290563

[ 16] 0x000000001847e5a5 bin\win64\pgo\m_lxe.dll+00320933

[ 17] 0x000000001847c140 bin\win64\pgo\m_lxe.dll+00311616

[ 18] 0x000000001847ba64 bin\win64\pgo\m_lxe.dll+00309860

[ 19] 0x00000000175e9525 bin\win64\pgo\m_dispatcher.dll+00038181 AutoPushingExecutionFrame::AutoPushingExecutionFrame+00002325

[ 20] 0x00000000175e998d bin\win64\pgo\m_dispatcher.dll+00039309 Mfh_file::dispatch_with_reuse+00000045

[ 21] 0x000000001a0eff4a bin\win64\pgo\m_lxe.dll+30146378 mwboost::archive::detail::pointer_oserializer<mwboost::archive::binaryTerm_oarchive,MathWorks::lxe::MatlabIrTree>::save_object_ptr+00774562

[ 22] 0x000000001846bc47 bin\win64\pgo\m_lxe.dll+00244807

[ 23] 0x00000000184b8f99 bin\win64\pgo\m_lxe.dll+00561049

[ 24] 0x000000001781ff80 bin\win64\pgo\m_interpreter.dll+00065408 inCallFcn+00000176

[ 25] 0x00000000e7e9ddd7 bin\win64\libmwsl_services.dll+02219479 slsvFEVAL+00001431

[ 26] 0x00000002b5956e3a bin\win64\stateflow.dll+15887930 SF::GraphInfoProvider::operator=+00010890

[ 27] 0x00000002b5eb345e bin\win64\stateflow.dll+21509214 SF::mx2str_write_str+00037422

[ 28] 0x00000002b5961b8d bin\win64\stateflow.dll+15932301 SF::sf_mexFunction+00002861

[ 29] 0x00000002b5961075 bin\win64\stateflow.dll+15929461 SF::sf_mexFunction+00000021

[ 30] 0x00000000fc634844 bin\win64\libmex.dll+00346180 MexRetrieveVersion+00003348

[ 31] 0x00000000fc634ba4 bin\win64\libmex.dll+00347044 MexRetrieveVersion+00004212

[ 32] 0x00000000fc618089 bin\win64\libmex.dll+00229513 mexUnlock+00024825

[ 33] 0x00000000175e9525 bin\win64\pgo\m_dispatcher.dll+00038181 AutoPushingExecutionFrame::AutoPushingExecutionFrame+00002325

[ 34] 0x00000000175e998d bin\win64\pgo\m_dispatcher.dll+00039309 Mfh_file::dispatch_with_reuse+00000045

[ 35] 0x0000000018470214 bin\win64\pgo\m_lxe.dll+00262676

[ 36] 0x000000001846bc47 bin\win64\pgo\m_lxe.dll+00244807

[ 37] 0x00000000184b8f99 bin\win64\pgo\m_lxe.dll+00561049

[ 38] 0x000000001781ff80 bin\win64\pgo\m_interpreter.dll+00065408 inCallFcn+00000176

[ 39] 0x00000000e7e7a768 bin\win64\libmwsl_services.dll+02074472 slsv::mxw::WarningHandler::operator=+00008808

[ 40] 0x00000000e7e8f80e bin\win64\libmwsl_services.dll+02160654 CMatlabCommand::execute+00000270

[ 41] 0x00000000e7e9df71 bin\win64\libmwsl_services.dll+02219889 slsvFEVAL_NoThrow+00000289

[ 42] 0x00000000e7e9e010 bin\win64\libmwsl_services.dll+02220048 slsvFEVAL_NoThrow+00000064

[ 43] 0x00000002ca62c605 C:\Program Files\MATLAB\R2019a\toolbox\stateflow\stateflow\sf_sfun.mexw64+00050693 mwboost::serialization::singleton_module::lock+00002517

[ 44] 0x00000002ca629a8b C:\Program Files\MATLAB\R2019a\toolbox\stateflow\stateflow\sf_sfun.mexw64+00039563 NoSetErrorStatusException::operator=+00010075

[ 45] 0x00000002ca63528b C:\Program Files\MATLAB\R2019a\toolbox\stateflow\stateflow\sf_sfun.mexw64+00086667 mexFunction+00003451

[ 46] 0x00000000fc634844 bin\win64\libmex.dll+00346180 MexRetrieveVersion+00003348

[ 47] 0x00000000fc634ba4 bin\win64\libmex.dll+00347044 MexRetrieveVersion+00004212

[ 48] 0x00000000fc618089 bin\win64\libmex.dll+00229513 mexUnlock+00024825

[ 49] 0x00000000175e9a66 bin\win64\pgo\m_dispatcher.dll+00039526 Mfh_file::dispatch_file_common+00000210

[ 50] 0x0000000017604083 bin\win64\pgo\m_dispatcher.dll+00147587 MathWorks::builtin_leak_assert_guard::builtin_leak_assert_guard+00000567

[ 51] 0x00000000175e9abd bin\win64\pgo\m_dispatcher.dll+00039613 Mfh_file::dispatch+00000045

[ 52] 0x000000001765a1d6 bin\win64\pgo\m_dispatcher.dll+00500182 mdDoMatlabFcnCall+00000122

[ 53] 0x00000001b318455a bin\win64\sl_utility.dll+00345434 SimpleUserException::~SimpleUserException+00000282

[ 54] 0x00000000e7e8f948 bin\win64\libmwsl_services.dll+02160968 CMatlabCommandNoWatermark::execute+00000056

[ 55] 0x00000001b3184f19 bin\win64\sl_utility.dll+00347929 slDoMatlabFcnCall+00000089

[ 56] 0x000000000e211b12 bin\win64\libmwsimulink.dll+18160402 SLGlue::isStateOwnerBlock+00228994

[ 57] 0x000000000e20f821 bin\win64\libmwsimulink.dll+18151457 SLGlue::isStateOwnerBlock+00220049

[ 58] 0x000000000e212061 bin\win64\libmwsimulink.dll+18161761 SLGlue::isStateOwnerBlock+00230353

[ 59] 0x000000000e1f2d83 bin\win64\libmwsimulink.dll+18034051 SLGlue::isStateOwnerBlock+00102643

[ 60] 0x000000000e1f31ba bin\win64\libmwsimulink.dll+18035130 SLGlue::isStateOwnerBlock+00103722

[ 61] 0x000000000e1f4b17 bin\win64\libmwsimulink.dll+18041623 SLGlue::isStateOwnerBlock+00110215

[ 62] 0x000000000e1b4b9c bin\win64\libmwsimulink.dll+17779612 StateflowAccessStateInterface::~StateflowAccessStateInterface+00037164

[ 63] 0x000000000e01863b bin\win64\libmwsimulink.dll+16090683 closeMaskEditor+00050779

[ 64] 0x000000000e018939 bin\win64\libmwsimulink.dll+16091449 closeMaskEditor+00051545

[ 65] 0x000000000e027161 bin\win64\libmwsimulink.dll+16150881 BlockSetLocation+00006337

[ 66] 0x000000000e023227 bin\win64\libmwsimulink.dll+16134695 closeMaskEditor+00094791

[ 67] 0x00000000da47a18e bin\win64\sl_lang_blocks.dll+07905678 SubsystemBlock::CheckSetRTWFileName+00004302

[ 68] 0x00000000da4797c1 bin\win64\sl_lang_blocks.dll+07903169 SubsystemBlock::CheckSetRTWFileName+00001793

[ 69] 0x00000000da4c2233 bin\win64\sl_lang_blocks.dll+08200755 SubsystemCopyContext::srcBdIsHighlighting+00007523

[ 70] 0x00000000da478d4e bin\win64\sl_lang_blocks.dll+07900494 SubsystemBlock::CheckPrmsAndCreateDlgPrmCache+00001118

[ 71] 0x000000000e018670 bin\win64\libmwsimulink.dll+16090736 closeMaskEditor+00050832

[ 72] 0x000000000e018939 bin\win64\libmwsimulink.dll+16091449 closeMaskEditor+00051545

[ 73] 0x000000000e027161 bin\win64\libmwsimulink.dll+16150881 BlockSetLocation+00006337

[ 74] 0x000000000e023227 bin\win64\libmwsimulink.dll+16134695 closeMaskEditor+00094791

[ 75] 0x00000002095565e5 bin\win64\sl_compile.dll+06383077 EvalAllBlockParamsAndModelArgs+00003605

[ 76] 0x000000020923eec4 bin\win64\sl_compile.dll+03141316 SLCompEvalAllBlockParamsAndModelArgs+00001828

[ 77] 0x0000000209284f1b bin\win64\sl_compile.dll+03428123 SLCompVCEPropStageTwoAndRemoveInactiveChoices+00010571

[ 78] 0x000000020928511f bin\win64\sl_compile.dll+03428639 sleCompileBlockDiagram+00000399

[ 79] 0x000000000db90bc9 bin\win64\libmwsimulink.dll+11340745 sl_pir::copyContentBetweenModels+00196761

[ 80] 0x000000000db876a1 bin\win64\libmwsimulink.dll+11302561 sl_pir::copyContentBetweenModels+00158577

[ 81] 0x000000000db87be0 bin\win64\libmwsimulink.dll+11303904 sl_pir::copyContentBetweenModels+00159920

[ 82] 0x000000000e23c32d bin\win64\libmwsimulink.dll+18334509 slstSetOutputPortRateID+00136045

[ 83] 0x000000000e241605 bin\win64\libmwsimulink.dll+18355717 SLGlue::PortSignalGenerator::isEmpty+00012405

[ 84] 0x000000000e248311 bin\win64\libmwsimulink.dll+18383633 SLGlue::PortSignalGenerator::isEmpty+00040321

[ 85] 0x000000000e247ab7 bin\win64\libmwsimulink.dll+18381495 SLGlue::PortSignalGenerator::isEmpty+00038183

[ 86] 0x000000000e27c445 bin\win64\libmwsimulink.dll+18596933 SLGlue::PortSignalGenerator::isEmpty+00253621

[ 87] 0x000000000daf0a82 bin\win64\libmwsimulink.dll+10685058 slAccPostBlock+00122338

[ 88] 0x000000000d96916d bin\win64\libmwsimulink.dll+09081197 QueryMLFcnTable_libmwsimulink+00098365

[ 89] 0x00000000175e6e0a bin\win64\pgo\m_dispatcher.dll+00028170 mdFindFunctionFromUserSpecifiedName+00016858

[ 90] 0x00000000175e8f49 bin\win64\pgo\m_dispatcher.dll+00036681 AutoPushingExecutionFrame::AutoPushingExecutionFrame+00000825

[ 91] 0x00000000175e80bd bin\win64\pgo\m_dispatcher.dll+00032957 Mfh_MATLAB_fn_impl::dispatch+00000045

[ 92] 0x00000000184731d9 bin\win64\pgo\m_lxe.dll+00274905

[ 93] 0x0000000018631ba2 bin\win64\pgo\m_lxe.dll+02104226 mwboost::archive::detail::oserializer<mwboost::archive::binary_oarchive,foundation::msg_svc::eventmgr::BaseEvent>::oserializer<mwboost::archive::binary_oarchive,foundation::msg_svc::eventmgr::BaseEvent>+00073902

[ 94] 0x00000000184793e1 bin\win64\pgo\m_lxe.dll+00300001

[ 95] 0x000000001863be3d bin\win64\pgo\m_lxe.dll+02145853 mwboost::archive::detail::oserializer<mwboost::archive::binary_oarchive,foundation::msg_svc::eventmgr::BaseEvent>::oserializer<mwboost::archive::binary_oarchive,foundation::msg_svc::eventmgr::BaseEvent>+00115529

[ 96] 0x0000000018478bd6 bin\win64\pgo\m_lxe.dll+00297942

[ 97] 0x0000000018637f30 bin\win64\pgo\m_lxe.dll+02129712 mwboost::archive::detail::oserializer<mwboost::archive::binary_oarchive,foundation::msg_svc::eventmgr::BaseEvent>::oserializer<mwboost::archive::binary_oarchive,foundation::msg_svc::eventmgr::BaseEvent>+00099388

[ 98] 0x00000000184785ab bin\win64\pgo\m_lxe.dll+00296363

[ 99] 0x000000001847e5a5 bin\win64\pgo\m_lxe.dll+00320933

[100] 0x000000001847db4c bin\win64\pgo\m_lxe.dll+00318284

[101] 0x000000001847c55d bin\win64\pgo\m_lxe.dll+00312669

[102] 0x000000001847c405 bin\win64\pgo\m_lxe.dll+00312325

[103] 0x000000001847c42d bin\win64\pgo\m_lxe.dll+00312365

[104] 0x00000000175e9a66 bin\win64\pgo\m_dispatcher.dll+00039526 Mfh_file::dispatch_file_common+00000210

[105] 0x000000001767252e bin\win64\pgo\m_dispatcher.dll+00599342 Mfh_error::lookup+00005234

[106] 0x0000000017672dcd bin\win64\pgo\m_dispatcher.dll+00601549 Mfh_file::dispatch+00000045

[107] 0x00000000184731d9 bin\win64\pgo\m_lxe.dll+00274905

[108] 0x0000000018631ba2 bin\win64\pgo\m_lxe.dll+02104226 mwboost::archive::detail::oserializer<mwboost::archive::binary_oarchive,foundation::msg_svc::eventmgr::BaseEvent>::oserializer<mwboost::archive::binary_oarchive,foundation::msg_svc::eventmgr::BaseEvent>+00073902

[109] 0x00000000184793e1 bin\win64\pgo\m_lxe.dll+00300001

[110] 0x000000001863be3d bin\win64\pgo\m_lxe.dll+02145853 mwboost::archive::detail::oserializer<mwboost::archive::binary_oarchive,foundation::msg_svc::eventmgr::BaseEvent>::oserializer<mwboost::archive::binary_oarchive,foundation::msg_svc::eventmgr::BaseEvent>+00115529

[111] 0x000000001848802c bin\win64\pgo\m_lxe.dll+00360492

[112] 0x0000000018488d13 bin\win64\pgo\m_lxe.dll+00363795

[113] 0x000000001848ae5d bin\win64\pgo\m_lxe.dll+00372317

[114] 0x000000001848a23f bin\win64\pgo\m_lxe.dll+00369215

[115] 0x000000001848a76c bin\win64\pgo\m_lxe.dll+00370540

[116] 0x0000000018477b6d bin\win64\pgo\m_lxe.dll+00293741

[117] 0x000000001847e5a5 bin\win64\pgo\m_lxe.dll+00320933

[118] 0x000000001847db4c bin\win64\pgo\m_lxe.dll+00318284

[119] 0x000000001846b6cd bin\win64\pgo\m_lxe.dll+00243405

[120] 0x000000001846adeb bin\win64\pgo\m_lxe.dll+00241131

[121] 0x000000001846ae5e bin\win64\pgo\m_lxe.dll+00241246

[122] 0x00000000184b6068 bin\win64\pgo\m_lxe.dll+00548968

[123] 0x00000000184b6016 bin\win64\pgo\m_lxe.dll+00548886

[124] 0x00000000184b90f5 bin\win64\pgo\m_lxe.dll+00561397

[125] 0x000000001786d62f bin\win64\pgo\m_interpreter.dll+00382511 inEvalCmdWithLocalReturn+00000063

[126] 0x00000000fb60fc64 bin\win64\libmwbridge.dll+00130148 mnParser+00001316

[127] 0x0000000017479518 bin\win64\mcr.dll+00890136 mcrInstance::releaseThread+00002552

MATLAB stack trace:

> In get_sf_block_port_info (line 21)

[Mark McBroom]

Your error is related to manipulating a string in a StateFlow chart. Did you recently add variables or logic dealing with strings?