Featured image duplication

I have a problem where my featured image on my courses page is appearing twice. Each image is directly above the the other one.
I have read the answers about having a featured image and also having an image in the page editing area. This is not the case. I have deleted all references to the image and whenever I add the featured image again, it duplicates.

https://www.courses.dumagueteielts.com/course/grammar-awareness-course/

The image for the course (on the course page is fine (singular image), but when you click on the grammar awareness page, the same image is duplicated.

Any ideas?