Hi Robert and thanks for getting in touch!
We certainly do our best to integrate with as many themes as possible, but there is always the chance that some are simply incompatible. That said, we build and test all our releases against standard WordPress themes (e.g. Twenty Fifteen) to make sure we’re at least setting the bar at WordPress’s own standards.
Have you tried switching the calendar template in Events > Settings > Display? It’s possible that using the default calendar template instead of a default page template could do the trick.
Otherwise, I would say that the theme author might have a better idea for why the default calendar template is being overridden by a theme archive.
Does this help answer your question? Sorry I don’t have a concrete solution for you, but I do hope this at least helps shed some light on what’s happening.
Cheers,
Geoff