@David-TP 

Answers to your questions

1. At the same time I have 13 online devices 9 on the main site and 4 on the guest site.  But only devices on the main network have the problem.  Both the main and guest networks have completely different network names and both have both 2.4 and 5ghz bands enabled.  Of these, there are 8 x wifi sockets, 1 x wifi thermostat, (these 9 devices are all controlled via tuya and there is no problem with them, also 2 x camera system, 1 x air conditioner (cameras and air conditioners have a problem and I keep disconnecting and connecting them, the most  air conditioning) and others. the device is a tp link archer c54 router, it also has no problem.

2. Deco is connected via an ethernet cable and the connection is stable. air conditioning and one camera system is only on a 2.4ghz wifi connection and one camera is via a cable to the archer c54  C 54 does not disconnect, but the cameras do, even if they are connected with a cable.

3. I did not add anything. But when was the update to the current latest version of FW, I do not remember if before the problem started or on the contrary, the problem started, I looked and saw an available update and performed it  . I don't remember that.

4. I will do this test, but at the same time since your answer the problem seems to have disappeared. I will wait until tomorrow and see when the problem returns I will try the test of turning off the 5ghz band on the main network.