Spirit Walker Bear Coop Crash.

Playing togheter (co-op) with a spirit walker causes the game to crash at times.
Got this error msg:

Fatal Error in
Metadata/monsters/companionBear/companionBearPlayerSummoned@40: Number shared states is diffrent on client and Server! Delta: 174

The crash seems to trigger only when the bear is "off-screen". I can't trigger the bug, so I don't know exactly what causes it, but so far I seem to have narrow it down to off screen and in combat. But not 100% since it has only happend 3 times so far, (in roughly 5 hours of game play, 1 time yesterday, 2 times today.)

Edit: I am not the spirit walker, the person I am playing with is.