Sensus Navigation Problems

[V60Powerrr]

Hello, so today we made a trip from Leeds to Reading, a distance of around 220 miles. We put our destination into the sat nav and were on our way.

Approximatley halfway through our journey we pulled into a service station and as we were once leaving again the sat nav began recalculating and then failed to recognise our position and showed us on the A5 when infact we were on the M1.

After failing to find an option to re-calibrate or synchronise the GPS we again pulled into the services but this time switched the car off completely and left it for 10 minutes. Shortly after switching back on the Sat nav showed us in the middle of nowhere but then suddenly picked up our location and showed us again in the services.

Allowed time after exiting the services to set the sat nav again and we were fine for the next hour or so until we turned off the M25 and onto the M4, going through the junction passing under another carriageway the nav again became confused and attempted to recalculate however it failed and again showed us travelling in the completely wrong direction and with no deviation. It seems it had failed to recognise our position or had not realised we had joined the route (as it would show the dotted line in the direction of the start of the route)

Was just looking for some advice or anyone who may have had any experience with their nav like this.

Thanks in advance
P.S. I apologise if this is in the wrong section but I couldnt find anywhere else to put it and I assume these cars are the ones most likely to have the nav in them.