@Peter-Burch-1-0 said:
Thanks @Nick-Carthew, that was the answer.
I imagined that in selecting 'Offline navigation', I was just giving MRA permission to use downloaded maps as well as any information it can get from our 'intermittent at best' mobile networks here in the UK. It never occurred to me that it would inhibit MRA from using the mobile connection (when available) to calculate routes. I think I selected it to stop myself getting all those annoying 'offline' messages when riding. I will need to reassess my tolerance levels for them, methinks.
I'd already posted this reply but, about 6 or 7 hours later, I can't see it yet. Maybe it's still awaiting approval, but I've no way of knowing whether that is the case or whether it got lost in the ether so here it is again. Well, part of it anyway. And now I've screwed myself over by accidentally hitting 'submit' after a few words so have to wait an hour to post again because I'm a new user. It ain't easy being a newbie.
Garmin devices are much better in this respect. It's possible to use the local map for navigation and planning whilst also getting live weather and traffic reports via the Tread app. which is then displayed on the Garmin device.