All the mining logic needs to be run on the server (Auth Proxy).
Client inputs Mine Action,: Switch has Auth(remote) → starts any local animations → RPC Server.
Server Event [run on server] … do all the mining actions/logic.
Last graph pic (Server Spawn Item)…
Actor spawned needs to have “Replicated” ticked.
Also, You do not need to Cast the output of a Spawned Actor. For validation purposes (did it spawn something?) just use Is Valid on the return, then set your current stack.