Ah maybe that's part of the explanation. Server is in Germany. Thanks
Viewing post in Treacherous Journeys jam comments
That's what I'm doing - no new info about the arrow is being sent from the time it is fired until it hits. Then when it hits it gets new info from the server and interpolates position. So if something is out of sync then it can suddenly shift quite fast in the end.
A better solution might be to add a hit effect and just let the arrow die at an appropriate time:)