Hi James,
Thanks for reaching out and also thanks for taking the time to search for similar topics in the forum. As you point out this is something that happened to many users lately, so I’ll try to dive into it and see if it’s a conflict with SEO plugins (Yoast in this case).
As you aren’t able to test for conflicts in your site, I’ll suggest you do a template override of the widget view to strip the hAtom classes. To do so you need to copy the file ‘list-widget.php’ from ‘wp-content/plugins/the-events-calendar/views/widgets/’ over to ‘wp-content/themes/your_theme/tribe-events/widgets/’ – you can find detailed information about this in our Themer’s Guide. Once you have the file in place, go ahead an edit line 31 as shown below:
// original
// modified
Please let me know if this works for you,
Best,
Nico