unable to add measures

I think this is the right forum; this seems like a bug to me.
Trying to add one bar at the end of this tune. I tried various ways, including saving and quitting & then re-opening. The screen shots show what happened - the tune is 96 bars long; I need one more. When I add, the file becomes corrupted. I tried inserting at a place not at the end to no avail. I'm currently re-doing the score in a new file (I copy-pasted everything, but of course I have to add all the barlines, first & second endings, etc. Very frustrating.)
Lenovo laptop, Windows 10