so i created a new profile in anki 2.1.52-qt6, and i have tried the steps i outlined above. there was no crash!
the crash was only occuring with my OLD profile (i.e. the profile which i had since the beginning).
however, when i exported the content (i used both types of export) from my OLD profile to my NEW profile, the crash started to occur again.
in summary, the crash does not occur on an empty/small profile. CORRECTION: the crash does not occur on profiles that have small/no repetition data (I have import a deck with 13k cards and no rep history. the crash did NOT occur)
i can now confirm that the crash does not occur (kind of) if you have a small/no repetition history.
steps i have taken (no crash steps):
delete history from the database
open the profile which had the crashes
do the crash-inducing steps i have outlined above
no crash!
However, if you do the following, you will get a crash (CRASH steps):
delete history from the database
open the profile which had the crashes
Check database and wait for it to finish
quickly press T to get Stats
close Stats (Esc)
crashed!
I don’t know whether you used empty profiles or not, but perhaps, what you can do in order to reproduce the issue is (unless you have already done that):
I have experimented with different collection/history sizes and even tried adjusting the code to alter the timing, but still have not been able to trigger the crash on machines here.