It seems to me that the game code design was not done with high network delays in mind. Probably design phase tests were only conducted on a LAN. I've played different games online on different platforms and had not encounter similar problems.
The problem is related to either browser specific or network driver specific handling of long polling HTTP packets as best I can determine. The game has a streaming system for incoming messages which control the behaviour of the game, so that it can update whenever a player makes a move, or a chat message arrives etc etc. The client sends a subscribe POST to the server which just sits there with no response generated until there is data to deliver.
It is my suspicion that these type of requests fall foul of driver management of outstanding HTTP requests - either they get put on a low priority queue, or are internally discarded in some implementations.
In order to get around this problem I will have to look at a websockets implementation to handle the streaming instead, which is my next priority because the game needs to be 100% stable. Please bare with me while these changes get implemented

Cheers, Paul.