Perhaps I'm missing something and perhaps this is what's supposed to happen, but it does seem very weird to me...
Last couple months I'm struggling with a huge data corruption issue (I have created another ticket for that issue) and I've run 50+ scrubs on my 30TB of data in meanwhile. I noticed some weird behaviour of scrub (of which the most important one is in the subjuct):
1) There is no log of scrub anywhere. I had to create my own script for this functionality:
2) Scrub CKSUM errors are cleared on reboot. Suddenly / magically your pool is healthy again after a reboot (but in reality, it may not be)
3) I once also had a SATA cable with a bad connection, which threw 1000+ READ and WRITE errors during scrub, causing scrub to flag the disk as broken and the pool as degraded. Also this was cleared during a reboot!! Without me taking any action in TrueNAS, a reboot caused TrueNAS to start resilvering the pool, with the same disk still in the pool! Luckily I did re-attach the SATA cable, so that resilver was actually ok for me. But that it started doing this without me saying that I fixed the problem, does seem very wrong to me...
4) I'm not sure how scrub works and this could very well be correct behaviour, but I noticed that after a reboot (and after unlocking the pool), scrub automatically "resumes". But it doesn't resume where it left of... for example, once my system rebooted around 70% scrub complete and then scrub resumed at 50%. But it is not always 20% that it jumps back or even not always at the same % that it jumps back. It seems very random. Together with the lack of logging, I also find documentation on the whole scrub process very lacking. I had to figure out with trial and error...