Hi there Jessica,
Thanks for getting in touch with us! I’m glad to help you out on this issue 🙂
First of all, great work spotting the conflicting plugin! I’m really not familiarized with it, and not sure what it does (unfortunately the link you provided is only for registered users in their site). Best I can say is reach out to them and report this issue, maybe they are even aware of it and have a solution. One thing that might be useful to include in the report is to check if featured images are still available in other posts types such as posts, pages or even products.
Can you please give me the name of the theme? Maybe I can find a related thread about this.
Please let me know if they are able to give you some more information,
Best,
Nico