Parent products ordered instead of child product

[Melmoi]

Hello,
I have a bug for a few days and it is random....
People make orders and when I receive the order, some of the items ordered are the parent product instead of the child product.
For exemple I have a swimsuit with child product (size S, M, L...), And the item ordered is the parent product with no size chosen.

I have changed nothing recently on the webiste so I wonder if it could be a server problem.
Have you ever heard of this problem ?

Joomla 3.9.18 / virtuemart 3.6.10 10211

[jjk]

If your website still is ...lingerie.fr, it might be time again to update VirtueMart (latest stable version 3.8.4) as well as your template and a few extensions. Accessing that site shows several javascript and stylesheet errors in my Firefox browser's 'Inspector' console.

You may also check if you have selected a different custom field configuration in the product settings for those products where the child product selection doesn't work.