I have installed the GMS 201 at a client and the push seems to work
occassionally and then stop working. Server continues to look fine and
nothing seems to change.

Could this be down to devices? As sometimes one will work and then not the
other. Sometimes both will not work. Could it be a WAN issue. or is there
something I could look at on the server logs etc. There seems to be a lot
of push queued messages and then a few hours later it goes through.