[friagram]

OnClientDisconnect
Why? When they disconnect their client entity is destroyed along with any attributes.

IsValidClient. Nope, also you are calling this in loops and inside calls after you have already called it. A simple isclientingame would do.

If you are so scared that replay and sourcetv will destroy your life, you can always use a player event to apply effects like player spawn or inventory application. Then you can also axe most of your other callbacks.