Was it just ZFS errors that you noticed? Did any of the SMART data also indicate the drives were bad?
I ask because when I first received my HL15, my unit marginal/bad cables which caused ZFS errors in my pool but the drives themselves were actually fine. It was really easy initially to point to the drives and took a lot of troubleshooting for me to figure out that wasn’t the case. From that perspective, I can appreciate you checking here on other possibilities.