ABRP gets lost !!

Just this weekend been using ABRP Premium in earnest to get used to it before a long trip to France.

Both out and back on a journey of a bit over 100 miles, ABRP has got lost! I've only slowly realised this when it started sending me down narrower and narrower lanes. It kept giving me directions, turn here, etc.

It was only when I stopped and opened up the app, that it showed I was nearly 10 miles away from the planned route!!

This was on both occassions in the same area with poor/intermittent mobile signal but I've never had this sort of problem in similar areas with Google or Apple Maps … In any case, my phone should still be picking up GPS positional information.

Any suggestions as to what is going on? Have I missed something in the settings?

Or is it a fundamental fault with ABRP