There should be a long post about issue with Xiaomi Zigbee devices maintaining connectivity due to associating itself to a Zigbee router that is not compatible with it.
A Zigbee Router is a Zigbee device that typically ac or dc powered. In its firmware, it has routing function that can help passing data from one device to another.
One thing that make this case unique is that the information about insecure join allow in some case the Xiaomi to be back in. Most people have to manually re-pair the device typically. It may still be possible that you may have different issue because of this.
I think the best thing to do when you are using Xiaomi is to surround your home with Xiaomi compatible routers.
The next best thing in mixed of compatible and non compatible router home is to have Xiaomi associate to one of those which compatible router and maintain that connection.
I could not find a thread with a list of compatible Xiaomi router. @veeceeoh may have that list. I also make Zigbee module that happen to be a Xiaomi compatible Zigbee router.