Aggravating this is you may never know. I’m on Linux so checking for background processes and other things is more or less second nature. One thing that is annoying is sometimes I’ll open a window and think it is closed and nothing seems to work. I’ve learned to minimize all windows to see if the thing just got moved to the back of the visual stack. If I accidentally minimize it the fun really begins because as a sub process it doesn’t show in the tool bar so I can bring it back up.
" if the thing just got moved to the back of the visual stack"
It could have been, except I exited and reentered many times to test other projects…
I work with 2 instances usually running, as it was during some of those tests…
Am using Version: 5.0.1+dfsg1-2~bpo9+1, release build in Debian linux. I have discovered through trial and error that if Kicad 5.0.0 repeatedly fails to act in the way you think it should one strategem to remember is to shut the program completely, and then restart it before retrying the action.
The 5.0 series is relatively new. There certainly are problems not found and fixed yet. It would be important to get them reported properly so that the developers at least would be aware of them and hopefully even fix them.
I know it’s difficult when you don’t remember exactly what you just did and even when you do, you can’t repeat it. But still. With a bit of luck someone else sees the bug report and can give more information or at least confirm the problem.
Is it possible that you still have the old kicad 4 github libraries setup?
Check your fp lib table and make sure it does not point to github directly but to local files.