I am not familiar with how other apps do it but our system uses an offline cachable terrain system that lets you take the data into the field with you and make route adjustments on the fly. It does not use internet once the data is loaded. My guess would be that other apps use Google Elevation Services for their terrain awareness.
As noted in the Terrain Awareness article, we use the SRTM data set which is available between 60N and 56S latitudes.
If you are outside these areas you are in fact out of bounds for our terrain service. The likelihood of you being that far north or south is unlikely though so it is possible you may be having a data related problem.
If you are trying to use our Custom Terrain feature make sure that the takeoff location and all waypoints are within the colorized area.
If you continue to have issues with it please email us a screenshot of the error and the state of the layout so we can see what is going on.