I’m not sure, but I bet that Predict Projectile Path by Trace Channel node is running in world coordinate space, but the Projectile Velocity is relative to the projectile actor’s forward X.
I noticed it doesn’t take any rotation inputs to see which way the projectile is facing. So that velocity vector input must be world space, not based on the direction the projectile is facing.
try making that projectile forward velocity be part of the character’s forward vector and feed the result of that into the Predict node. On the other hand, that doesn’t explain why it would be correct on the server, so I’m not sure if that helps.