custom taxonomies not considered in frontend?

Dear author, i work with event manager pro for an event portal.
events manager uses custom taxonomy for event categories.

i discovered following behavior, placed also to event managers support page (but they claim to use wordpress standard behavior – and plugins like this should do it right):

Dear support staff,

thank you for the information. I’d liked to try out this plugin.

Sadly, in the backend it seemed to work:
o choosing subcategories on 2nd or 3rd level brought up proper events, when i filtered the event list in the backend afterwards by main event category.
o but in the frontend, when i called /events/categories/main-category/, it showed still nothing.

=> I think it does depend on events manager, how it reads out entries for this taxonomy. Or wordpress behaves generally different in backend and frontend and the plugin author did not consider that.

All best, Thomas

Do you have a clue why your plugin works just in backend, not in frontend with this custom taxonomy?

Thank you, Th.