If you rollback to v.16 and the problems go away, it’s the new v.18 firmware that’s the problem. Easy to go back and test (you can always upgrade again to v.18):
https://community.tablotv.com/t/tablo-update-2-2-18-problem-recording/14444/19
It certainly makes sense that the four-tuner model is more demanding than the two-tuner one, so maybe these problems aren’t as manifest there. For my part, I’m sticking with the old tried-and-true v.16 with only minimal, occasional problems until v.18, or v.20 some day in the future, gets fixed.