Okay, so I'm struggling.
I am still having some issues with 9.2.6, but it doesn't seem as bad as 10b1.
It seems that when I play a recording back while it's still running, I get a lot more data errors. This happened this evening, but I didn't notice while it was running, so maybe it's always happened. Having checked the actual recording file, there was a massive amount of garbage after the actual programme, which may have coincided with when I stopped the playback.
If something records in the middle of the night, no data errors.
So, is the RPi4 just not up to playing back a recording while it's running? Is the problem that the MicroSD card isn't fast enough (SanDisk class 10)? Could it be something stupid like birds landing on the aerial?
Next up is to plug a second Pi4 in for playback, and just have LE9.2.6 on the 'server'.
Any more ideas for debugging this?
Seems to be happening on LE9.2.6 and LE10b1, but definitely worse on LE10b1. Happening on multiple TV tuners. Aerial hasn't changed. Happens with two different microSD cards.