Sorry to hear that! The usual reason for Xiaomi / Aqara devices dropping their connection is that they aren't compatible with one or more repeaters (as fully explained and covered in this thread) and the only sure-fire way to resolve this is to stop using the offending repeater(s).
If you've decided you don't want to deal with that, I can say that in addition to my Aqara motion sensors I picked up some Iris V1 motion sensors on eBay at a cost comparable to the Aqara ones. They are just a bit slower but work great otherwise.
