I don't know about this. We have a 0.5Z13 dedicated host running that started complaining about that "host didn't receive UDP packet" starting last wednesday. Maybe something happened prior to that day that changed something. I don't know if we used the server on the couple of days before that wednesdey, but since that day we can't join our server and I have to set my own dedicated server. I am pretty sure that nothing has changed on the host side and that this may have something to do with the latest client side patches. Of course, I may be wrong.
I haven't been able to contact our host guy lately to update it to the latest version, maybe that would fix it.
EDIT: I forgot to add that we had been using that server during the last weeks without any problem. My last race on that server was on november 12th.