jamieb's issue is not uncommon - WBS are still struggling with an issue where you are handed off to another tower that is close enough for your modem to see it, but too far for traffic to travel - hence the 'stallled' connection, forcing a manual disconnect and reconnect.
I have the exact same issue with the Northcliff and Randburg base stations - on Northcliff I get decent speed, 5 lights and 100% connection strength on Randburg no speed but still 5 lights and 100 connection. Annoying thing is that Northcliff passes me to Randburg every 5 minutes.... 20+ disconnections this afternoon alone....
The solution suggested by the call center is to place a metal object (tray or similar) on the one side of the modem, 'shielding' it from the unwanted tower - just put the tray north, east, south etc and test for stability.... not entirely sure that is a long term solution.
So I also sympathise with those users still struggling with issues - I am one