if you use the OpenTopoMap layer with the plugin, you may have some problems since August.
The reason is that the tile server of the OpenTopoMap project is in a maintenance mode, and apart from that the URLs for the tile server have changed.
There are new https URLs, and the old http URLs have changed, too.
Since it is likely that there may be some more changes to those URLs i'm currently not doing a new release of the plugin.
If you need the OpenTopoMap layer, (and you have the latest plugin version installed!), you can replace the gpxtrackmap.php file in \plugins\content\gpxtrackmap with the version attached here.
In this new version the OpenTopomap URLs have been changed to match the new https syntax.
NOTE: you should RENAME your current version to gpxtrackmap.php_old or similar before testing with the version attached here, so if anything goes wrong you can delete the new version and just rename the old version back to gpxtrackmap.php!