featured image not working

The plugin works perfectly except the event featured image will not “stick.”

I click the “set featured image” and it always defaults to highlighting a blank image. I instead click the image I want and hit save, but…it doesn’t work. I’ve tried to upload a new version of the image. I’ve tried saving and then editing. But no matter what, it won’t stick.

I should note that the “featured image” works fine on regular blog posts but no matter what I try, it will not work for events.

https://www.treeoflifependants.com

https://www.ads-software.com/plugins/upcoming-events-lists/