Cart not adding items correctly

Hi, I am new to the forum so please excuse if I am ill-informed 🙂
We use learnpress and are experiencing a problem with additional items adding to the cart when people want to purchase a course. This does not happen with all courses and also not with every individual e.g. I can add a course on my side now and experience the issue, while my colleague then does the same and doesn’t encounter the problem. This occurs when you are logged in as a user and also when not logged in:

When you click on some of our courses the “Add to cart” button does not display, but “view cart” displays without you adding the course. when you then “view cart” there is a number of courses displaying in the cart (eventhough you didn’t add them). It is always the same courses and to the same amount. As I mentioned, this does not always happen and also not with all users. I was on the phone with a client yesterday and she logged in with her login details (for the first time) and also had the specific items in her cart without adding them.

Could this be a browser issue or what can it be?

Any ideas on how this can be fixed will be appreciated.

Thank you!

The page I need help with: [log in to see the link]