Kwikset Zigbee locks pair, then leave the network

Okay, so I just got some zigbee modules that are supported by zigbee2mqtt to replace the flaky Z-wave ones.
I attempt to pair them as instructed (hit the A button 4 times), and it interviews okay, pairs okay, then suddenly leaves the network seconds later.

Any idea of what’s going wrong? I’m using a sonoff zigbee USB stick with the latest Home Assistant and the latest stable zigbee2mqtt. Sadly I do not own another zigbee stick to sniff the traffic with.

The USB stick has the latest firmware, too.

Thanks!

Updating this: They seem to pair despite leaving the network? But they are unresponsive.