The same thing happened here. All of my artifacts were removed from my belt, but at least we didn't lose the belt itself. It shouldn't be too hard to get back the knife because they put some next to you in the "ALBRT" bonus map. The knife and the black key are the most tiring artifacts to get back, but as long as you downloaded 0.16.0.2 before it was removed, you can get infinite sodas from the vending machines to aid you in making Cleany's item trail. Good luck getting a lock pick to get your key, though.
I realize you have gotten those artifacts back by now, though, so don't worry about my message.