Character rotations can diverge between clients and client/server briefly under packet loss and using bOrientRotationToMovement

At some points the rotations will diverge briefly while the client and server attempt to rotate to the orientation direction by going different directions about the rotation axis.

Open 3rd Person Template or another project using bOrientRotationToMovement setting in CharacterMovementComponent.

Enable 5% or worse packet loss ("Bad" network setting).

Have one character move around and back and forth until the rotation diverges. Easier to see by adding a visible arrow component to the mesh.

See https://udn.unrealengine.com/questions/577400/player-character-rotation-replication-and-packets.html