Users can't see login page -during peak times & random u

[MessWeb]

Hi,
I am having problems at one site of four - some users cannot connect to the system correctly - it shows limited or no connectivity on their wifi connection although the wifi link itself is strong and the connections to the switch / server are fine. It seems to only happen at peak times, and only affect a few people, almost at random.

At one point I thought it was an overheating issues but having improved airflow, it was fine for a week, then suddenly went poor again. Any ideas warmly recieved.

The affected users can't even see the initial login page, it seems as if the dispatcher isn't dispatching correctly?