Problems reading Mi Flora sensor

[stetho]

I have a number of Mi Flora sensors around my house which I was reading with ESPHome. I decided to have a play with room-assistant and it works quite well detecting phones in the house (Using a batch of 3Bs I had spare). So I added my Mi Flora devices to my config but all I get in the logs is

error - undefined: <PLANT_NAME_HERE>: skipping message as received data corrupt: RangeError [ERR_OUT_OF_RANGE]: The value of "offset" is out of range. It must be >= 0 and <= 10. Received 12

I've Googled various NodeJS errors with that error - value of a thing is out of range - but none of them have helped. I'm also inclined to think that if this was a bug in RA someone would have mentioned it by now. I've even been round and put new batteries in the Mi Floras just to be certain.

The Pi in the back garden is in a box to keep it dry - it has no trouble detecting phones but displays this error for the Mi Floras. Inside the house the Pis have a clear line of sight to the Mi Floras with the greatest distance being about 3m.

Anyone know what might be wrong?

Thanks

Steve