View attachment 4831107
You can see here that the belt slot is empty, but the gun is still on my chest. I'm wearing the cargo pants [Jeans_01], which include a belt. This is how belt slots show without a belt. The other jeans require a belt. I've tried both ways. With these jeans and other jeans with a belt. The other guns can go on my back, but when trying to place them on the belt slot, none can be placed.
Belts are busted in this update, I haven't been able to get them to work at all.
I don't think your issue is related to the belt though.
You should be able to swap between primary weapons with or without a belt.
Just for shits and giggles I loaded up my save and was able to swap the UMP45 with no issues holding the #1 key.
I can only assume this is a weird inventory bug and you're probably fucked xD
If you want you can upload your save -
C:\Users\x\AppData\Local\TheParasites\Saved\SaveGames
And I can see if it works or stays bugged on my end.