Yes I get the same problem, I can't join perpheads on the first try but on the second or third it usually works. If it doesn't I just restart gmod.I have the same issue that occurs, however only does it when I join a 'new' server or restart Garry's Mod and try to join PerpHeads.
I've just tried re-joining. It's either a connection problem with you and your internet service provider or just your computer / laptop.