I don't know the precise cause, but it seems to be related to network instability. I had a similar issue when I first got my Roamio last year. I tried to run via Powerline Ethernet adapters. Tivo/Tivo streaming would work sometimes with HD menus. Other times it would revert to SD menus when browsing he remote Tivo, but would allow Multi-Room streaming of shows. And still other times, it would be in SD menus and not allow Multi-Room Streaming. I spent about a week cycling through modified network setups to try and isolate the issue. Eventually, it became apparent that something with with the Powerline adapters was causing instability in the network. I switched to MoCA and haven't had a problem since.
It's entirely possible that there is something wrong with your Actiontec router and causing network instability.