This bug happens when my character is full of loot (anything works as far as I tested). I get frame drops when performing actions such as opening doors, switching/pulling out a gun, climbing ladders and jumping.
I have noticed that this bug is strongly related to how many open inventory spaces I have. For example: If I have 2 guns on my back, and I pick up a third gun, I get a permanent frame drop until I drop that gun or make room for it in my backpack, this happens on every server, modded or vanilla. I made a short video showing the bug:
This happens every single time when I gather a large amount of loot, and is 100% reproducible on my end.