Attach Pawn to Pawn replication

I got a tank. Basicly the problem shows if the client posseses this tank and i try to attach the server char to the tank. he should sit on top. What happens is that the server stops his movement replication from time to time on the client. He stops rotation updates and from time to time he flickers / get invis.

Most of the logic is inside the controller. The attachement is a multicast inside the character:
(i also tried other combinations like server side attachment but nothing seems to solve the problem)