@mrjj Thanks for posting that exact screenshot; it made me try switching to the 5.12.0 install I still had (since I saw your file path wasn't 5.12.1), and that in turn led to me noticing 5.13.0 is out now too.

This turned out to be specific to 5.12.1 (and maybe further specific to msvc2017_64, not sure).

No more crashing in any of my different test cases or my original app now, without changing anything in my code. I feel pretty silly for spending so much time coming up with a lot of different attempts to fix my code over the past few days, but I did learn a few new things about Qt at least.