That map layer appears to be the Apple Maps data which we have no control over. Make sure the 3rd party map source is selected. If you saved a mission for an area and the tiles downloaded they will be present.
The map control is the bottom slide out on the left. Then tap Basemap. Then select '3rd' to enable the saved layer.
It does look like you are trying to download a really big area though which might be problematic unless you are using your own 3rd party tile source.