Canon… I think that canon is spawned at level start, and not in your character blueprint…
You just go near cannon and want to shoot with E right?.. Thats not possible because you dont own that canon because its spawned on server, and server owns “everything” but client owns only what is spawned in his blueprint…
Check this: Engine-breaking physics + network - World Creation - Epic Developer Community Forums (you need work with player controller)
Its my topic where i tried to control lifts, its same like you want to control canon i think…