So when try place a soph backpack the game crash
crash-2023-05-23_16.58.41-client.txt
it seems that is a modernfix problem
somthing about multiple threads accessing colleciton that's not made for multiple threads

After some code analysis this appears to be a bug in Sophisticated Backpacks, and in theory can happen without ModernFix installed as the affected code was not modified by ModernFix. I commented on the other issue P3pp3rF1y/SophisticatedBackpacks#775.