Ok, I did a clean install off both the 7 days to die client and dedicated server. I then updated both to 16.2 and installed valmod + bigger backpack on both, following the instructions to the letter.
Once this was done, I started a new random world and loaded in. Everything seems fine, but when I put an item in the bottom row of my backpack, and log back on, it’s gone.
I’m 100% sure the files are in the right place.
I've got no idea what's wrong and it's really bugging me.
Edit: Yes I've turned off EAC, if not the server wouldn't start. Also, I managed to get this to work fine on 16.1, but I had the same issue until someone found a bug in the dlls...
Edit2: It works perfectly in single player. This is only a problem on the dedicated server.