I’ve tested it on a smaller document with only two layers and the same issue occurred.
HOWEVER, the issue is thankfully now fixed!
I toggled the Freehand Selection tool mode from vector to pixel and these were the settings.
I tried turning Feather to 0, toggled back to vector, and the issue has gone away!
I have no idea if pixel mode settings are supposed to affect vector settings but if so, I assume this is a bug. I’ve also moved Feathering back to 8 on pixel and toggled to vector again and the issue comes back again.
I will say that as far as I know I’m pretty sure I’ve always used the Freehand selection tool on vector mode up to this point and only had this issue until now. The issue also persisted even I tried updating to the latest version of Krita right before I tried making this thread.