My 3rd Deco unit suddenly stopped connecting to the internet. All of my devices that have been connected to that unit for many months suddenly indicate "connected without internet." Strange thing is that I'd if I switch them to the guest network, they connect just fine.

I reset the unit and it worked normally for a few hours but then the problem came back.

When I'm connected to the guest network, the Android Deco app shows the unit as online and working normally but if I reconnect to the main unit, I cannot find anything using the app. 

Using the guest network is not an acceptable workaround because I have devices that must be on the same network to function properly.