lol I wrote you a response, much of which is wiped out by your updates!
Newly remix version:
XG1's? Hmmm, not too many posts about em on here! Any chance this is a known issue with XG1's->Minis?
Does it happen on all channels? In every resolution (of the source signal/channel)? Does it happen with the minis set to output different resolutions? When you play back recordings are the visual glitches in the same places? Hmmm... every few seconds... are you running anything with a large motor, like a dehumidifier, furnace, treadmill, etc that might be putting out electrical or rfi interference that the (theoretically) less shielded/robust Minis might be being affected by?
Have you rebooted everything... the XG1's, minis, moca adapter, cable modem, router, etc?
No open taps on your splitters? All coax cable ends in good shape? All coax connections tight? No ancient cables? Does the coax run near any possible sources of interference?
I assume the minis came from your cable co? Are they running version 20.3.8 of the tivo software? Are the XG1's running whatever their latest software is?
You listed the PHY values, but are you getting Moca errors?
PHY values are the raw data rate for data xfers over the coax. There is overhead for transmitting ethernet data over coax, with additional checksumming, etc. So 275phy rate = ~175mbps. HD shows only need like 20mbps, so you're good there!
If you move one of the minis to where one of the XG1's are at, using the same cables/connections, do you see the same problems?
Because the XG1's can stream cleanly to each other, the following I now put less weight on:
You said your "splitter" is rated for 1ghz, but you have two splitters in your layout.
Test your POE filter by putting it "between" two moca devices to verify its blocking moca signals.
Temporarily try the POE filter on the coax input of your cable modem. (Rarely) Some cable modems hate Moca signals and cause problems.