I moved back to single player from a multiplayer run to visit the merchant which was unavailable in my friends town. Upon returning to multiplayer everything I purchased was gone and my old equipment had been reequipped. The new equipment was not in my inventory or stash, and all of the gold I spent was also gone. It didn't return after returning to single player or restarting the game. I haven't tried to recreate this bug.
#Items bought in single player disappeared when changing to multiplayer.
wild veldt
normal rose
The underlying cause of this is when the game saves, or rather, doesn't.