That is a common message. The guide should finally fill in within a few hours. Don't worry about it.
It does smell like a software issue. Maybe temporarily swap a small box with the big box and see if the problem moves or changes? Tighten all the connections leading to the small boxes? Any degradation noticeable with picture on the small boxes?
I heard it was a signal strength issue with everyone stuck at home. Sounds reasonable. Ours has come back but it took days not hours. We'll see how long it lasts. Our audio cuts in and out sometimes as well.