Blank spot on gps maps

[Occy]

I have the 78s gps loaded with mapsource. On the last couple of rides that i have done and gone thru a specific area ie Claremont side of Wynberg hill ( m3 ) the map on gps disappears and starts up again on the N 1 around Century City area. All gps shows is the major roads N1 N2 etc. Out of the "black hole "gps and loaded maps work fine. Any suggestions to rectify this. Have tried looking for updates for gps but aren't any.

Thanks in advance

 

[Moondog]

 

[Heimer]

 

[Occy]

 

[Bump]

 

[Mikie]