TiVo Roamio OTA - Working, but no display

Interesting behavior last night...which seems to have fixed itself...

But as we all know, nothing truly every fixes itself, so I assume this behavior will come back...

I have a TiVo Roamio OTA and a TiVo Mini connected to it.

When I try to connect to the main box, I see the TiVo screen for about a second or two, and then it disappears to a completely black screen. I tried power cycling it...same issue... I tried connecting and reconnecting the HDMI cable...same behavior... The front panel led indicators blink when I use the remote, so I know the box is "alive" and responding...

If I go to the connected TiVo Mini, it behaves as expected...

This morning, the main box started working normally again...

Any ideas what's going on? I couldn't fix it last night to save my life... and I do anticipate the symptoms to return at some point...