I am also having this issue. Compiling in xCode 11.7 fixes the issue - but obviously that is not a good long-term solution. Does anyone know if xCode 12.5 fixes this (and iOS 14.5) ?. I have not tried it yet, but its kind of random and hard to replicate on-demand.

So I am running xCode 12.4 on iOS 14.5 and I can replicate this on demand. In our app we use afnetworking to get a load of data and save it to core data. If I do a force quit while this "sync" is going on (asynchronous) and then go back into the app and then let it "resync" the data it eventually crashes. Not always at the same point. As to why? I have no idea what-so-ever - but at least I can replicate it on demand. The only fix I have right now is to use xCode 11.7 to build the app. I cannot crash it. I have tried in 12.5 but not yet replicated the issue - but per the prior post it seems it is there too.

so I can now replicate in 12.5 running on 14.5 ios. Here is what i know so far: I can replicate it if I force quit my app while it is syncing data into core data. then if I go back in quickly it crashes. If I leave it a while (between the force quit - or I go back in again after the crash) then it does not crash. It is as though that there is something left over from the force quit that it does not like when I go in and sync data into core data again. super annoying and very puzzling.