I might have a solution! : )
leaflet is used for OpenStreetMaps. It can also be downloaded here:
https://leafletjs.com/
When I extract and copy the latest version to a new folder in “event-organiser” on my webserver and change event-organiser-register.php to
wp_register_script( 'eo-leaflet.js', EVENT_ORGANISER_URL."NEW-FOLDER/leaflet.js" );
wp_register_style( 'eo-leaflet.js', EVENT_ORGANISER_URL."NEW-FOLDER/leaflet.css" );
(you have to replace NEW-FOLDER) then everything works perfectly fine without any external sources. You also don’t have to reinstall anything.
I guess EO updates may override this, but for now I’m happy with this solution.
Thanks for the great Plugin.