I am having the exact same issue since updating to DumaOS.
The WiFi just dies often and every device in the house connected via WiFi either gets the exclamation mark with the “no internet” message or cannot connect altogether. I have noticed that this happens more often when more than 2-3 devices are connected and using the connection at the same time (there are 6 devices connected with WiFi total in the house and all of them are connected with a static IP).
What I normally did to fix this was accessing the router settings using a LAN connected device and disable WiFi and enable it back on, but changing the channels that other people in here suggested also works after checking just now (my channel was set at 8 before that I noticed was the less congested in the area, have not checked if there is a pattern that sustains the WiFi functional longer with specific channels).
To be honest, I do not think it’s a hardware issue since so many of us have the issue by now and since a simple change in settings fixes it instantly. Possibly an update that will give us the option to select Auto as a channel option will be a good start start to check possible solutions as Fraser stated above. Hoping for a quick update, will be checking here often.
Also, a big thank you for all your quick replies in the forums and for the work you did on DumaOS in general, I absolutely love it despite its minor issues.