You have “Left Mouse Button” which is coming from the client calling a Multicast function, you should first have it call ServerFire (Run on server) then have the server call MulticastFire to call everywhere.
The client can not directly tell other clients what to do, only the server can.
I don’t see all the relevant code so I can’t be sure there’s not another issue, but if that doesn’t work I’d also make sure you’re only dealing with replicated functions with Net Owners (or things owned by them).