I think I have answered my own question. It seems that TotalMix stops displaying meters when the Digiface AVB loses sync. It had been synced to its first input stream, but was losing sync overnight, which somehow didn't affect the audio. I don't understand that. But it did stop the metering. I now have the Digiface AVB synced to word clock. It can't lose that.
A weird side effect I mention for AVB users who may also struggle with mysteries trying to get hardward from different manufacturers to work together. Now the RME and M64 have word clock sync, and the Ultralite is synced to a stream from the M64. But when I hooked word clock to the RME, the output of the Ultralite was phasy and distorted, even though it said it was synced. I had to set the Ultralite sync to INTERNAL to make it sound correcct. I definitely don't understand that. It says it is synced to 48k somehow and audio output sounds correct.
M1 Mac Mini/Sonoma/Digiface AVB -> Motu AVB Switch -> UltraliteAVB/M64/SSL AlphaLink MADI