Really not sure what that could be - generally proxies have caused save issues for us in the past... That kind of intermittent, possibly-time-related sort of error could be any number of things. At least it does actually save again though, it would be bad if saving stopped completely! My guess is that once the proxy has some sort of timeout on "active" connections, so it tries to give you the same information again instead of a valid new save return, then once you say essentially "no, do it again" it figures out that you should have a through connection after all and goes back to not getting in the way.
But that's just a theory and not a sanctioned technological diagnosis... Also, can I be allowed to be a little happy that you play for that long? That's awesome