I’m making an assumption that you have your pcie slot available - any chance you’re willing to pick up an HBA for around the same cost that you got this M.2 port multiplier?
Most of the drive you have are seagate, which requires some additional translation for smart values:
smartctl -a /dev/sdx -v 1,raw48:54 -v 7,raw48:54 -v 195,raw48:54
In the above example, values 1, 7, and 195 are translated to something humanly readable. Change & add/remove -v #value here#,raw48:54 as needed. For some drives you’d want to translate pending/current sectors, raw read errors, reallocated sector, etc etc. The value # aren’t set in stone as 1/7/195 - these are just the values for my seagate drives.
Before @winnielinnie gets a chance to suggest it; any chance you’ve recently run a few passes of memtest?
ZFS doing its best to keep things alive 