I have this exact same problem as well on Jun's loader 1.02b, DSM 6.1.5-15254-Update 1, DS3617xs. I had issues still on earlier version as well, 15047.
I am running ESXI 6.5, a Dell H200 flashed to IT mode, passing the card thru to XPE as JBOD with the intention of having xpenology manage the RAID. The disks are detected and I can put data on it, and it does say "SMART Status Normal" nder Storage Manager > HDD/SSD, BUT when I click one of the active disks and click "Health info" I get the same prompt as above: "Not available" so I am not sure how reliable that SMART status is.
Did you find a fix or solution??