We are playing 3-person multiplayer through Steam, and got 3 or 4 crashes yesterday in as many hours, seemingly whenever people are using the stash or talking to vendors/merchants. Crash reports have been sent through the game reporter.
The behavior seems very similar to this old post, which references something lost from the old forums:
https://old.reddit.com/r/Grimdawn/comments/k832qg/multiplayer_npcinventory_crash/