There's nothing relevant logged, and the server still crashing in maintenance mode points more to a hardware issue, could just be overheating, or power related, since a rebuild will use more power/cause more heat.
Reformatting the emulated drives will delete all data there, and IMHO nlikely that the disks are the problem, I would check CPU temps and/or try again with a different PSU, if available.
I would recommend resetting the current stats and monitoring the pool for future issues, since it can be much harder to resolve a problem if a bad or dropped device goes undetected for some time.
Look in syslog for a list of corrupt file(s), those should be deleted/restored from a backup, then re-run a scrub to confirm there aren't any more errors.
Possibly, could still be a RAM issue since memtest is only definitive if it finds errors, since you have multiple sticks try with just one, if the same try with a different one, that will basically rule out bad RAM.
Try running another filesystem check, that still looks like a filesystem problem to me, if it doesn't help, I would backup and re-format that disk, to make sure the issue is resolved.