@satek,

A few things that I would try changing as a result of the logs you posted.

Try either disabling or manually setting QoS to what you expect from your ISP

Try to Disable the Band Steering Option.

Do all of the Deco Units in your Network Reboot, Is the Main Node Rebooting or Does it Simply Lose its connection? The LED status lights on the node will indicate which happened.

Given that there were errors for file directories, you may want to perform a factory reset if the behavior persists. Otherwise, double check that you are using the most up to date firmware.

Lastly, if the main node is the only node connected to the network, does the behavior persist?

If you feel there is an issue with the firmware of the device, and not a setting: there was a beta firmware for the X55 posted to our global forums here, which may be of use to you.