Hey Angela,
Sorry for the delayed response here!
1. Question One
I’m curious, do you mean that in your wp-admin you do not even have the “Featured Image” metabox as shown in this screenshot:

If this is what you mean, then does anything change if you use the “Screen Options” tab to reveal this metabox? This process is demonstrated in these two screenshots:
• https://cldup.com/bboWaFhNO4-3000×3000.png
• https://cldup.com/MghDpmAZLA-3000×3000.png
2. Question Two
If that “Featured Image” metabox does show up on edit-event screens, then can you clarify when the bug actually arises? Does it manifest as:
• The “featured image” metabox shows up, but when you try adding an image using it, the image disappears when you save the event?
OR
• The “featured image” metabox shows up, and it saves the images you choose fine. But it just doesn’t show up on the front-end?
3. Question Three
Can you include your “system information” in a reply on this thread? Here’s how to do that → https://theeventscalendar.com/knowledgebase/sharing-sys-info/
If you address each of the 3 main questions here, that will give us a much clearer picture of your issues and a lot of information to work with to facilitate the investigation of their source.
Thank you!
George