No internet access through Unifi?

Question

Computer networks

Goodnight! The situation is as follows, there are several rooms, in all of which access to the Internet is provided by Unifi access points. The system has been working great for over a year now. If there were any problems, it was due to an incorrect voucher or a change in the poppy address of the client, etc. trifle.
But a week ago, complaints began in one of the rooms, saying that the Internet is either there or not. I decided to try to diagnose remotely. I went to the controller - I see the client, but the address is like 169.xxx.xxx.xxx. They reloaded his card - the address was normal. Then the nonsense with the voucher began, after entering the number, the message "an error occurred" is displayed, without details. After some time of dancing with a tambourine, everything started up. I see the client on the controller, he received the address, the traffic went - there is Internet. But then all activity disappears and the Internet falls, while at the point it hangs as if nothing had happened.
He spat, arrived at the place, took out his netbook, picked up the first time, put Google on ping and went to deal with the client. There is no Internet, the signal is full. I already tried to break through the IP address with my hands, I looked at ipconfig - everything is in order, they waved the wi-fi adapter to another just in case - anyway, the Internet, that is, it suddenly disappears. And one computer would be fine, but several people have this problem on different pieces of iron. Who has a laptop, who has a stationary with an adapter. All with one voice say the same symptoms. And the most interesting thing is my netbook, for the hour that I spent at the facility I never glitched and did not fly out, which means that the access points are working properly. Of course, I assume that this is a herd feeling of "users", but somehow they sing painfully smoothly.
What could be the jamb, what else would you recommend to see?