Unable to see the pull downs/tools in Simulink Diagram for MATLAB Simulink 2019b ONLY

This is an intersting one, hoping I can get some help. I have installed on a Red Hat Enterprise Linux OS version 7.3.2 simulation host machine MATLAB versions: 2017b, 2019a, and 2019b. Due to fielded product support, all these versions are needed. When I load a Simulnik diagram (a model) generated by myself or by someone else on the same machine in either 2017b OR 2019a, the Simulink Diagram loads w/o issue, and the pull-down menus (File, Edit, View. etc) and buttons (Save Diagram, Library Browser, etc.) are visible. However, when I do the same for a model (generated by another, because of this issue), I cannot see any of these pull-downs or buttons. I am currently working remotely and connecting via a Windows 10 laptop using the Windows Remote Desktop (RDP). Again, this is ONLY the case for 2019b Simulink diagrams; both 2017b and 2019a work w/o this issue. The error I see when loading a 2019b diagram is: Failed to load URL:

https:localhost:31517/toolbox/dig/web/toolstrip/html/viewID=(lots of numbers/letters)&config=sl_toolstrop_plugins&checksum=(lots of numbers/letters)&snc=GKTESX

Error: ERR_TUNNEL_CONNECTION_FAILED(-111)

I have done some searching on MATLAB Answers on this error/topic/issue. I do not beleive this is a proxy issue, as I have confirmed that the proxy settings for 2017b, 2019a, and 2019b are all identical: all are "Use a proxy to connect to the internet" + Proxy Host XXX.XXX.XX.XX and Proxy Port XXXX; all Test connection w/ Success!; 2019a, 2019b are Use system web browser UNCHECKED (2017b this is not a checkbox option); all are Command: firefox.

I found this existing answer: https://www.mathworks.com/matlabcentral/answers/382910-when-i-excute-my-model-it-always-give-me-this-massage-failed-to-load-url-https-localhost-31515-too

I have followed thru some of the debug steps that Suraj Mankulangara provided on on 23 Feb 2018.

1. uifigure executes as expected for all three MATLAB versions 2017b, 2019a, and 2019b: a figure box opens titled Untitled Window.
2. c = matlab.internal.webwindow(connector.getUrl('/')) did have differnces between the MATLAB versions; I can provide them in a follow-up to this question.
3. c.show for all MATLAB versions opened a [connector service] window and stated "The connector service is running."
4. [a,b] = system(sprintf('"%s"',fullfile(matlabroot,'bin',computer('arch'),'MATLABWindow.exe'))) did NOT open a MathWorks page; instead, it yielded a = 127 and b = '/bin/bash: /opt/matlabr2019b/bin/glnxa64/MATLABWindow.exe: No such file or directory; this response was, however, consistent across the versions (as in, 2017b, 2019a, and 2019b all yielded this No such file or director response, with different pathing based on the version).
5. I skipped this step (>> !ping localhost; >> type(fullfile(getenv('windir'),'System32\drivers\etc\hosts'))), as this is (I beleive) a Windows-cenric debvug step...this issue is on a Linux system.
6. I skipped this step (>> !ipconfig) because I can confirm access to external internet, and because the network configuration, firewqall, and adapter configuration used to get external should be agnostic to the MATLAB version.
7. connector.isRunning yields ans = loical 1 for all MATLAB versions.

At this point, I'm pretty stumped. Firefox web browser has a configured proxy to access the internet, using an autmoatic proxy configuration URL. Moreover why would the Firefox settings negatively impact MATLAB 2019b but not 2017b or 2019a.

Any help greatly appreciated.

Respectfully,

Mike C.

[Michael Caputo]

This has been resolved by user(s); a fix was found and instantiated. Including this detail for benefit of MathWorks personnel and others. Was issue with MATLAB 2019b using Chromiom and Chromium's adherace to environmental variable no_proxy. If no proxy was previously instantiated (for terminal sessing via .bashrc file) and did NOT include localhost and 127.0.0.0/8 (as configured for our systems), the banner (i.e loaded webpage) would fail. This was independent of MATLAB proxy settings to reach out to the web. It was also not possible for users to source another's .bashrc file for testing of this. At this point, we do not have resources to debug further (as to why source of a more correct .bashrc file) did not resolve the issue, but have included fix steps for benefit of MATLAB/users below.

1. (if previously instantiated) un-comment the proxy related “exports” in you .bashrc file
2. Update the “no-proxy” line in .bashrc to iinclude: export no_proxy=”<yourlocaldomain.com>,localhost,127.0.0.0/8”
3. Save .bashrc
4. Run: source ./.bashrc
5. Check that the “no_proxy” variable is set correctly with: echo $no_proxy
6. Confirm that the output is “<yourlocaldomain.com,127.0.0.0/8”

Again, specific to MATLAB 2019b.