I have had difficulty replicating some of the problems with captions. But I just had the problem you describe occur. This is in a very small test project with very few captions. Resetting the workspace and various other strategies produced no change. It was occurring and only one of several sequences with captions. Saving, closing Premiere, and reopening help, but only after I made a couple of small changes and then things started working again.
Changes made appear in the caption panel in the small image to the left, but do not appear in the timeline.
Changes to caption streams are saved in the project file, in a complicated difficult to read format. It is not clear to me yet whether all changes made are saved even though they don't appear in the timeline, or not.
The particular sequence I had a problem with was one that I had duplicated from a different SRT file, but that may have had nothing to do with it.
Adobe does not announce updates before they're actually made, but in another thread, we've been told that there will be one very soon. I believe that we will see fixes to some of the caption problems, but we never know for sure.
Thanks for all the investigating you did. I'm glad you were able to see what I'm talking about.
I did see that thread on the update. I'm sure hoping that it fixes these ongoing issues that I'm having. Like I said, I have spent extra hours working on fixing bug issues with Pr. There have been many.
I actually started another Captions file. It is working so far (fingers crossed). I tried this in the past and it didn't work. Who knows.
Please update Premiere Pro. Several bugs related to captions were fixed. Let us know if it is working now.