Xiaomi sensors are in a separate category. The original model is not certified to the same zigbee home automation standard that smartthings uses. It doesn’t check in in the same way. It doesn’t work very well with repeaters from other brands, either. But these are very cheap and actually pretty well-made. But it’s a slightly incompatible device, so there are some quirks. And one of those is that they can, indeed, disconnect from the network. Particularly if they try to route through a repeater.
A lot of people are using them just because they are so cheap. (Commonly under $10 per sensor) but there are risks because of the lack of certification.
At least once, and I think twice, all the Xiaomi sensors stopped working after a smartthings platform update.
I wouldn’t call them crappy, because I think they work with their own gateway quite well, and they don’t promise compatibility with anything else.
But at the same time, if you want to use them, you have to do a lot more network planning than you do with ZHA certified devices.
And none of this has anything to do with “device health.” You run into the same issues with the Xioamis whether you have that turned on or off.