We get this a lot now. Used to get it all the time in early version 4 builds, Went away for a long time, but seems to be happening again. Might be just coincident.
If we hard code to a proxy with its IP it is never an issue, if we have it pointing to the FCDN of the server after the connection is backup it sits on "408 Request timed out - Retry in 60 seconds", but never does. If we hit "Register" it is fine.
We don't want to hard code to the IP of the server as we have SRV entries on the Domain Name and some failover/load balancing setup. If we hard code to 1 server we loose redundancy.