Lately, clients connected via capsman are getting addresses, but pings are not coming until you reload capsman, what happened?

Question

Mikrotik

The structure is as follows:
There is a domain controller, the DHCP server is raised on it
Capsman is configured on the central mikrotik, the points distributing wifi are connected to the central via cables, of course. Worked steadily for several years. But in the last 3 months, such a problem began to occur: the client clings to the point, the IP receipt time is updated on the DHCP server, but the client does not ping and the Internet is not available to it. Moreover, this does not happen with all clients, most of the others can work normally at the same time. Reboot of a point to which the client clings, does not help. Helps off / on capsman. I already overloaded everything, but there is no sense. For more than a year, the firmware was not updated, no new equipment was added, no settings were changed, but this problem began to arise. It can work for 2-3 weeks without problems, but it happens that 2 days in a row there is a problem with different clients.
What to do? Where to look?