I describe both the issue and the solution (which I could not yet found here).
My issue was that mapsmarker icons did not show both on the site and in the admin dashboard. The cause was the \wp-content\plugins\leaflet-maps-marker\.htaccess
file is not compatible with Apache v2.4.
I had to change Allow from all
into Require all granted
for it to work again.
Probably it’s good to implement it as a change in the new version.