This issue also is happening to me. I tried flushing permalinks and cache. My specific issue is trying to use the ‘events’ slug for a different page. It seems Events Calendar forces the ‘events’ slug to the calendar page.
I was able to temporarily fix by going back to version 4.6.9 for the-events calendar and 4.4.21 for events calendar pro. Hoping there is an update to fix this soon.