Products not being added to table

Hi support team,

We have found that when using the website in incognito and sometimes logged in the adding products is not working as it should, not adding the product to the table or not adding a second product.

Can you please check why this is happening?
URL to site – https://wordpress-314780-5205978.cloudwaysapps.com/product-category/all-our-contemporary-sofa-beds/

Best Regards
Ruben

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