Navigator jams at same point on route each time

I occasionally drive the same route to and from London from the South Coast of the UK. Although I know the route, I have Navigator on in case I hit a detour.

The last four times, on the return journey, the phone has jammed at the same point on the route +/- 800 yards. It's the link road between the M23 Southbound and the A24.The only way out is to reboot the phone. I have tried restoring the SD card but it still does it. It sounds crazy - how can this be? It never jams anywhere else or on any other route. No trees to hide the satellites etc.

Any wisdom would really be appreciated.