I've looked at another thread regarding a similar issue, but my script does not have the same issue.
ServerScript:
GunFired:FireClient(player, CurrentAmmo, AmmoLeft, CurrentMag)
ClientScript:
GunFired.OnClientEvent:connect(function(CurrentAmmo, AmmoLeft, CurrentMag)
I've never encountered this issue before, and I'm not sure where I'm going wrong.

1 comment
This means the "GunFired" event is not being directed right, make sure you have the variables set up correctly.