You may have Zigbee repeaters on your network that Xiaomi / Aqara are incompatble with. The best thread to read about this is this one:
I would specifically start with a recent post I wrote about the same problem of someone’s Door/Window sensors not staying connect here, and then continue reading the posts following that.
If the hub “knows” what’s called the ZigBee ID for your motion sensors, then there is a method to get them manual rejoined to the network.
First check for the ZigBee Id by logging into your hub’s IDE, click on the My Devices tab, then click on the name of the motion sensor in the Display Name column. This takes you to the device details page for that sensor. You should see something like this:
As long as you see a value for the Zigbee Id, then you should be able to rejoin the sensors with these steps:
- In the IDE for your hub, click on Live Logging so you can see when the sensor reconnects
- In the SmartThings Classic mobile app, go to the My Home tab and press the + icon to “Add a Thing”
- Long-press the reset button on the sensor itself, until you see the LED blink. Same as when original pairing it, if you see 2-3 short flashes, it has successfully reconnected, and if there’s just one longer flash it hasn’t reconnected yet. If you see the longer flash, keep short-pressing the reset button every 2-3 seconds until you see the 2-3 short flashes in response. When the sensor has rejoined the network, you should see log entries. If unsuccessful after 1 minute, I’d suggest starting over with step 2.
If you’re able to reconnect the motion sensors, keep in mind that they will be in “location test mode” which means after motion is detected, they will reset and can detect motion again in 4-5 seconds, as opposed to the normal 1 minute wait for motion to be detected again.
Also important to understand: The DTH has nothing to do with connection problems. Again I recommend reading the post I linked to above.