D'oh! I was cursing #TomTom for enshittifying the cloud service associated with their #satnavs as my real time traffic and stored places wasn't working on the move - but for some inexplicable reason a #Xiaomi mobile phone I use as a backup device and hotspot had got mobile data shut off.

This still permits the hotspot to be activated without any warning which makes absolutely 0 sense) - but of course the navi can't access these services as there is no valid IP route w/o LTE data!