December update on the SSD/PCIe cards for my 7,2:
First, HP replaced all my dead SSDs so I now have 8TB of them again!
Second, I replaced the OWC 4M2 PCIe M.2 NVMe SSD adapters with Sonnet M.2 4x4 PCIe adapters. I now have 16TB of storage again, jiffy quick storage thankfully. I've put 4 HP EX950 2TB SSDs on one Sonnet card, and 4 Samsung 2TB 970 PROs on the other. They've been running fine for over a month.
The OWC cards and HP SSDs started failing much faster than that, so I'm cautiously optimistic about the current setup.
I still think the double sided aspect of the HP SSDs contributed to the OWC card and SSD failures in spite of OWC's statements to me to the contrary. I have a feeling that single sided SSDs may work OK with the OWC card. Either type seems to work fine with the Sonnet card which has different thicknesses of heat transfer material that are installed depending on which thickness of SSD you put in.
The 7,2 is now working the way I hoped. I can use it without the ominous feeling of impending disaster. Maybe it will continue?
Hopefully,
Tom