Hey Lee,
Sorry for the delayed response here!
This is not something “stupid” on your end!
In fact, it looks like a JavaScript conflict emerging from either your theme or another plugin on your site.
I would recommend doing each of the steps recommended in this article → https://theeventscalendar.com/knowledgebase/testing-for-conflicts/
After EACH STEP in that process, take another look at what happens when you hover over those events…do the tooltips show correctly, or continue to be broken?
Let us know what you find!
Thank you,
George