This map?
https://www.gpsfiledepot.com/maps/view/1/I don't have any experience with this, but it was created by the site administrator here, so hopefully he will respond. You could send him a PM:
https://forums.gpsfiledepot.com/index.php?action=profile;u=1What you describe could happen if you did not install the entire map on your GPS (MapInstall and Mapsource allow you to choose how much of the map to install).
It could also happen if there is a problem with the way the map was created.
It could also happen if you install too many maps on your GPS at the same time. Garmin units have a limit to the number of map segments they can access (these are the small "tiles" that make up the whole map). If you exceed this limit, some parts of some maps may not work. The problem is specific to the exact maps you have installed so it's impossible to say exactly what will happen.
Older handhelds only access about 2000 map segments. Newer models typically can access about 4000 segments. These are the total of all maps installed on the GPS, regardless of whether they are in internal memory or a card. There are not standard segments sizes, that's up to the mapmaker.
But, for example, if you install one of Garmin's own 24k maps, you will already be close to the segment limit typically.
What GPS are you using and what other maps are installed?