400mb internet service in home. Tablo connected to router, but wireless to fire tv
Sounds like you are dropping wifi signal to the fire tv. The Tablo is sending a relatively high amount of data to it (video is always the most demanding on wifi). I’d try going into your router settings and giving the fire tv the highest priority you can.
The other thing you can try to test this is to lower your resolution and see if the dropouts still happen.
I run 1080 60 on my Tablo and had dropouts. Once I gave my fire tv stick priority on the router, those circles have all but disappeared.