@John-B-1, no, I understand completely that it is difficult to take screenshots in heavy London traffic. Especially with everyone driving on the wrong side of the road
(a joke with a beard, I am guilty...)
I suspect you were driving inline, without offline maps downloaded and no live internet connection (or very bad signal). Is that feasable? In that case the app can not calculate a new route.
Also I noticed (pretty randomly) that the app cannot connect with the online platform after having switched between different networks. Something that is very difficult to pinpoint. In such a case a force close and restart of the app fixes things. But also that takes some fiddling, so best done in a parking space.