This is probably related to the offline maps issue.

My choice for navigating is the OS map on my android phone.  Having created a long route (~50 miles) I went over the whole route with the OS map selected, while I had wifi available, hoping the phone would at least temporarily store all the necessary map sectors.

It worked for about 20 miles, then the maps all disappeared leaving the blue route on a black screen.  I stopped for a coffee and used the wifi there to repeat the trick for the rest of the route.  Once again, after about another 20 miles all the maps disappeared.  So it appears the alternative maps can't be used for long journeys.

Anyone any ideas?

A further comment, although I have the Cycletravel maps for much of England available offline, I don't think the CT map has enough contrast.  Designers always need to imagine (or deliberatley look at) their creation in black and white or grey scale.  If it is readable then it will be OK in colour.