I think this error started when I did upgrade firmware from 3.4.3 to 3.5.0beta3.
At first I didn't upgraded DuetWifiServer and then first time this error happened.
So I concluded that most likely problem was with old version od Wifi server so I upgraded to latest version.
And I did it twice because first time I was not sure if it finished correctly because error apared again.
I'm not home at the moment so I can't check if DuetWifiServer is 2.1beta4, It is 2.1 just not sure if it is beta4 or what.

Yestereday, in 3 hours got this error twice.
I'm using WiFi extender because signal was to weak for direct connecting to router if that have any importance.

I have the same issue, Duet 2 WiFI v3.5.0-beta.3, Duet WiFi server 2.1beta4 and DWC 3.5.0-beta.3
Currently can't connect to board trough USB, not enough place for straight USB plug, waiting 90 degrees USB plug.
Reseting WiFI (M552 S-1) is hard trough PanelDue because error was spaming PanelDue with popup messages and it's not posible to press Console button when errors poping constantly.
Any news about that error?