Just for the record, as I have been wrapping my head around it for the past few days when I was trying TVHeadend on Raspbian (Buster) on RPi4 (with WinTV-dualHD DVB-T dual tuner). While working with DVB-T2 channels I registered a significant number of "Continuity errors".
It seemed to be a bit better on USB2 ports, though the errors were detected on both (USB3 and USB2) ports, not only in TVHeadend log, but also visible in the image as an intermittent pixelation and stuttering. For a comparison I have been running a same tuner (WinTV-dualHD) on the same source (both tuners connected through a passive Y-splitter) connected to RPi3B+. While even RPi3B+ showed some continuity errors, there were less of them, and they were not visible in the video (and I suspect they were mostly related to "channel switching").
RPi3B+ was also running Raspbian (Buster) updated to the same state and TVHeadend installed from the repo.
Eventually, I was also testing the same tuner (used with RPi4) on GTKing (Beelink, Amlogic 922X) with CoreElec 9.2.5 (and built in TVHeadend).
The conclusion was:
1) My tuner was originally set to isochronous mode as reported by `eeprom-tinker` (pointed out in this thread).
2) Using the tool I was able to switch it to bulk mode.
3) When running the bulk mode on RPi4 on both USB2 and USB3 ports it has led to significant reduction of "continuity errors" (though not to complete elimination), to the point that there is no degradation visible in the video.
The bulk mode also seems to improve an error rate on GTKing where previously it did not work very well on USB3 ports (but worked fine on the one and only USB2 port).
The only mystery is that the same tuner in isochronous mode works well on RPi3B+, which, technically, should be less capable (slower) than RPi4.
