Ceiling light loosing wifi

Good day!
I have 4 Yeelight Ceiling light devices ( 450 mm and 480 mm) at home and I have an issue that they constantly loosing connection with WiFi, mostly in the middle of the night (but some times during daytime also). In such state they are reflected as offline in wi-fi router page, in Yeelight app in Mi Home App.
What worries me most that after going offline they does not reconnect to wifi, but remains in this state till restart (power-off / power-on). After restart immediately reconnect to the network.
All devices have latest firmware (2.0.2_48) updated from Yeelight application. Wifi was tested with 3 different routers (asus rc87u, keenetic ultra, keenetic speedster) with the same result.
Wifi router is located on a distance from 2 to 10 meters from Yeelight Ceiling light devices but distance have no correlation with the connection. It looks like Yeelight device goes to sleep /standby and switch off wifi module.
All devices are in LAN mode.
Can you please help me resolve the issue. I can provide statistics, logs or any information required to test what is going on.
Best regards,
Vladimir