Child product is *sometimes* being replaced with parent product in the cart

[flippertricks]

Hi!

I have some parent products with custom fields, to create child products. The parent product should not be orderable and "please select a bodysuit size" message appears (and 'add to cart' button does nothing) if a size isn't selected.

In the last week, when a buyer adds a child product to the cart in frontend, it is sometimes being added correctly to their order, and for other buyers sometimes (somewhere, somehow) it is being reverted back to the parent product in the cart (or at least it appears to be a problem at the 'adding to cart' stage, as our payment transaction confirmation emails also only mention the parent product). This parent product should not be orderable (and we then have to chase up that buyer to find out what size they want). We've received two orders from two different buyers, each for a child product which is derived from the same parent product - but in one case the child was added to the cart, and in the other case the parent product was added to the cart.

I've tried replicating the problem myself, but everything appears normal when I try - the problem is intermittant.

Could this somehow be due to buyers using different browsers or devices? This has only started happening at some point last weekend and I haven't updated any components for our website in that time, so this hasn't come about due to updating anything.

I'm using Breakdesign's Stockable Custom Fields plugin, who I've messaged but haven't heard from yet. I'm unsure if the problem is related to either Virtuemart or the SCF plugin, or something else entirely?

Any help is much appreciated!

Example product being ordered, which sometimes has the parent product added to the cart: https://moonbump.com/products/silicone-fake-pregnant-bellies/fake-pregnant-belly-7-8-months-silicone-m5-p

Joomla 4.4.8
Virtuemart 4.2.18
Breakdesign SCF plugin 1.8.0
PHP 8.1.31