‘No internet available’ on one device

Switched to fiber about 6 weeks ago. Continually get the subject message about every 15 minutes. After rebooting the TV it works as expected until the next time. I tried ‘forgetting’ our wifi network as suggested previously. That worked for a few days but now it’s back to no internet available.

Only happens on one TV, the one we watch for the most part.  
We are ready to go back to cable.