In case anyone is interested - and at the risk of inviting trouble - I seem to have fixed this. As suggested here ...
It is possible to force a reboot according to the handbook but I have not bothered to do so yet.
... I did a factory reset, and after around 10 days the error has not recurred (I was getting it every 3-4 days before that).
If anyone else tries this, a few warnings:
- The reset removes all Android settings, including those related to wi-fi & bluetooth, plus stored trip data. It doesn't remove radio pre-sets.
- You need to re-install the Honda App Centre, so you need wi-fi working and a good data plan on your phone.
- Before re-installing the App Centre, you need to first set Android's security settings to accept apps from non-approved sources. If you don't do that, you are invited to do so after downloading the update ... but then the only way forward is to download it again.
Of course, all of this should have been fixed by the dealer before I collected the car. The fact that most people don't seem to have the problem but some do suggests there are differences between dealers in how PDIs are carried out.