If you are encountering issue that downloaded offline maps are not shown on main map screen in GPX Viewer this may have several reasons. Solution which will solve most of the cases of this issue is as follows:

1. Uninstall GPX Viewer from your device.
2. Restart your device.
3. Install GPX Viewer from Google Play Store again.
4. Firstly try downloading worldwide offline map and see if it is working.
5. If worldwide offline map is working try downloading other offline maps.

If this does not solve your problem. Please create ticket at our support system https://support.vecturagames.com/gpxviewer.