@Alexey777 

Have you tried statically assigning a static IP on the problem phone?

Another thing I remember is that on Android 10 it introduces a feature where it randomizes the MAC address. Try and disable that to see if that may be causing issues.

I think this may be the procedure how:

1. Open the Settings app.
2. Select Network and Internet.
3. Select WiFi.
4. Connect to the UT wireless network (UT Open or EDUROAM)
5. Tap the gear icon next to the current wifi connection.
6. Select Advanced.
7. Select Privacy.
8. Select "Use device MAC"

@Tony Thank you for your reply! 

I've turned off random MAC in my WiFi settings on the phone and I've also added my device MAC to static DHCP clients table in my router. 

Directly after reconnect to the Deco mesh WiFi network the problem has disappeared. 

I will continue monitoring how it works further. 

Thanks!

@Tony 

So after some days of testing, unfortunately, the problem persists and I'm unable to contact to those devices being connected to another mesh AP. It is a strange problem, because it is isolated currently specifically to my phone. 

A PC, other phone,  work fine. However I don't test them as much time, as my phone. 

The only workaround is to reboot an AP connected to those devices, then for some time my phone can connect, but later the problem appears again. 

My phone currently has static IP configuration in the WiFi network settings.