jkBuckethead

It appears it may in fact have been a power problem. Eventually the PSU died and all the drives went down. I'm thinking that my random failures may have been warnings of the ultimate failure.

I wanted to replace the PSU, which looks like a modified SFX power supply with just two drive power cables and a super short 24-pin. For a short time I did run it with a standard PSU sitting outside of the case, but I could not make a permanent PSU swap. The enclosure was built such that the PSU cannot be removed without significantly disassembling the case. The case is 100% riveted so tearing it apart and trying to put it back together would have been way more trouble than I care to bother with.

Instead, I bought a QNAP TL-D800S. I connected it to my existing LSI HBA and it worked perfectly. I did not try the HBA that came with the enclosure. The enclosure is expensive but seems well-built. Toolless trays are always appreciated. The only downside is the cost, which increased $100 shortly after my purchase. The SATA version is $100 more than the USB-C version, presumably because of the HBA card and cables that are included. I wish they offered a bare version of the enclosure without these extras but no such luck.