Perhaps you’re one of the lucky ones. I should mention that I didn’t have the “unavailable” Device Health status all of the time - just a number of times. When I looked for information about it at the time (late last year), what I found was that Device Health only officially supports devices that use SmartThings DTH code.
Having worked extensively on the bspranger/Xiaomi DTHs, I can say that the code of setting up the device health check time interval is exactly the same as it is in the a4refillpad DTHs.
Based on recent troubles that people have been having, though, I think maybe it might be a good idea to remove that code completely until SmartThings announces formal support of Device Health for devices using custom DTH code.
SmartThings has publicly admitted troubles with Device Health last week, and they claim that everything is resolved now:
Also, from the SmartThings Status page:
