Problem with the map

I have seen similar when there were two maps enabled that had overlapping coverage? What maps do you have and any chance they cover the same area or overlap, does the blank area occur with different zoom levels?

The map is only this one. This is true at all zoom levels.

These were my examples on a 530 and 3 years ago, caused by overlapping enabled maps, both NW France, one was OSM NL format and other BBBike Garmin "Onroad" but they somehow interfered, enabling only one, did not matter which, fixed the issue. If yours is not the same cause then I don't have any further suggestions and given the lack of anyone else suggesting a cause you had better contact Garmin Support. When you get it fixed come back and let us know how.

PS The 2 big cart wheels on the right of the right screenshot are Rennes (top) & Nantes (bottom) and the intersection of the 2 red "N" routes to the left of the left screen is Brest. What map are you using, if not Garmin perhaps you should look to it’s source?

I had the same today. I guess it's similar to https://forums.garmin.com/sports-fitness/cycling/f/edge-1040-series/373233/edge-1040-map-stuck-randomly-while-navigating, because swiping back from and forth to the map screen solved the issue temporarily.