Hi there,
I did what you suggested. I disabled all plugins (except for WPML, because thats the page that is needed, the french version of the events calendar) and the events calendar plugin, no change.
I then switched to the default theme, 2014, and still no change…however, one differece now, is it navigates to the home page when looking for that page (however, I think thats a default function within the theme to go to the home page is a page isnt found).
SO, not really any change to report. Please continue to look into the issue…thanks:)