Issues with non-light Hue devices

Been having a lot of fun with zigbee2mqtt and Home Assistant with a mixture of OSRAM and Hue globes - everything there works without a hitch.

Unfortunately, I’m having problems with a couple of Hue motion sensors.

I bought two on sale and paired one - it worked immediately and I happily set up an automation to control a hallway light.

The following morning, the motion sensor had stopped reporting to the hub. I tried re-pairing it but now I get this error message:

Jun 28 16:31:21 raspberrypi npm[447]: zigbee2mqtt:error 6/28/2019, 9:31:21 AM Cannot get the Node Descriptor of the Device: 0x00178801032a84b6 (Error: Timed out after 10000 ms)

I just tried setting up the second motion sensor. It worked for a matter of minutes before it stopped. With this one, I’m constantly getting this message in the log:

Jun 28 16:37:25 raspberrypi npm[447]: zigbee2mqtt:debug 6/28/2019, 9:37:25 AM Received zigbee message of type 'endDeviceAnnce' with data '"0x00178801032a8357"' of device 'SML001' (0x00178801032a8357) of endpoint 1

Any suggestions of what to try to get them working?