Properties section becomes blank and grayed out

I added some functions to the editable functions area of my .mlapp file. I realized that one of those new functions required a new Property of the app. I went to add one and discovered that both the Property menu at the top of App Designer, and the properties section in the Code Browser, were grayed out. Nothing I could see that I could do to change this. I tried saving the file, in case that would help stabilize things. No help. I closed the file and reopened it. Even worse. Now the Properties and the Functions section in the code browser are completely blank, as well as grayed out. On the second try, things have developed to the point that in the Design View I just see spinning wheels in all the components.

I found a potentially useful error message in the main Matlab window. It said, "unable to find app.ReviewTab". But in the non-editable section of the code, I plainly find

            % Create ReviewTab
            app.ReviewTab = uitab(app.TabGroup);
            app.ReviewTab.Title = 'Review';

And in the properties that correspond to app components:

ReviewTab matlab.ui.container.

Tab

Has anyone else seen this state of affairs? Has anyone found a way back from it? Failing that, has anyone figured out what causes this disease and how to prevent it? Because otherwise I'm just going to be continually going back to a previous version in version control, and walking on eggshells lest I trigger it again! Any help appreciated.

[Dinesh]

II tried to reproduce this behaviour in R2023b, but I couldn't. Could you please share the ".mlapp" file?

Answer 1

[Kenneth]

Okay, I found it. I was overlooking a tiny little error indicator in the upper right corner of the code view.

What was REALLY going on is that I had pasted in a callback function after editing the text in Visual Studio code, and I inadvertently wound up with two copies of the same callback function, one created the standard way, and one pasted into editable code. Oops! That was a tricky one!

I untangled things by Remove Callback, which made my file functional again, and then I removed the copy in editable code, copied its contents, and pasted those back into a properly created Callback.