Got it working eventually. But think my MiaoMiao is faulty. It only seems to run for a day or so before it needs reset.
I'd been using blucon for a while before changing to mm 3 weeks ago. First 2 weeks were fine, then when I changed sensor, it was really sketchy, dropping out every 30 mins or so for a couple of days.
I remembered reading a thread between the xdrip and mm developers and they were talking about the "air gap".
It seems that if there is a gap of more than literally a millimetre or two between the mm and the sensor, the nfc is so weak, it won't read properly.
I had a look at it on my arm, and it had slipped down a bit.
Reattached, and made sure it was jammed right up against the sensor, and it was fine after that.
The error logs don't go back that far on mine, so I can't show you an example, but it's maybe worthwhile having a look at your error logs (right hand side, three vertical dots, View Event Logs, tick Mid).
In the pic below, see the line which says, "We have all the data that we need 363 checksum_ok = true"? If yours is saying "false" at each 5 min read, it might be that the mm is just not pushed up tight enough against the sensor. There was some other error text with it, I can't remember now exactly what it was, something along the lines of "Sensor Not Found". If you're seeing that sort of thing, I reckon it's maybe because it's just a millimetre or two too far away from the sensor.
If it's not that, then, hmm, sorry, don't know.