Okay, I think I have progress.
I created folders on my NAS for timeshift and recordings. Figured it wouldn't hurt to use that for all disk bashing. Obviously I had to mount them in LibreElec.
At the same time, I dropped down to a single tuner plugged directly into the aerial, cutting out the signal booster. This seemed to work fine, so I dug out my previous signal booster and switched back to that.
Touch wood, I haven't had any data errors.
Of course, I don't know which of these things has had the biggest impact. I'm inclined to suggest the signal booster, although I was getting good signal reported.