WiFi problems with all my Tasmota's and ESPHome's

Hi.

Anyone have tips how to trace cause for this problem:
All my Tasmota’s and ESPHome’s will drop out from my WiFi network and all of them nearly at same time! Sometimes there is many days without problems but sometimes same thing will happen multible times at same day.

OpenMQTTGateway (BT) will not have any connection problems, but ESP32 Bluetooth Proxy will have.

Scheduled WiFi router restarts will not help…

WiFi router: RT-AC88U with latest Asuswrt-Merlin