Hi!
My apologies for taking so long to reply. If possible can you verify for me that you only have The Events Calendar activated and aren’t using Events Calendar PRO? and that you are talking about the Events List widget?
If so you may want to look into if the website’s current theme is modifying the $wp_query object. In the widget we use the object to construct our query for the events to display and your theme may be conflicting with our widget’s logic.
I hope this gives you a place to start! If my understanding is incorrect please let me know and we can investigate further.
Thank you,
– Matthew