Compatibility Support Mode Issue

A further update.  I can now only get the secondary SSD to work if it is plugged into the Asmedia SATA port  AND disable CSM. This  SSD does not show up at all in the UEFI . I am suspicious about the SSD. Some months ago, it failed with total loss of data, but I was able to reformat it.

A bit more detail. I have

Fatal1ty Gaming K4 MB with 1700X CPU
Samsung 850 Pro SSD boot drive with W10 connected to SATA 3_0
Adata SU 800 SSD secondary drive connected to SATA3_1 or Asmedia SATA port
WD green 3TB secondary drive connected to SATA3_3

All drives are GPT and formatted NTFS. EFI and operating system partitions exist only on the Samsung drive.

I've been having problems with the SU 800, which is used exclusively for data.  Once there was a complete loss of data, but I was able to reformat the drive. More recently, the computer stopped booting and I discovered that I either had to remove the drive or put it on the Asmedia SATA port with CSM disabled to allow  booting to proceed from the Samsung SSD.  Otherwise, I get to the initial splash screen and the system basically hangs (if I recall correctly, it shows "a2").
I have noticed that the SU 800 drive does not show up in the  UEFI, though the others do. It would seem that there is some kind of incompatibility between this particular SU 800 and the B350 chipset.  I have updated the firmware on both the motherboard and SU 800, and reset the motherboard firmware, but this has not helped. I've also tried a different SATA cable, again with no success. Although I can't find any indications of SMART errors, I am inclined to blame the SU 800 at this point as the other storage devices have been trouble-free.