configurable product – “Only 0 Left” message has suddenly appeared after upgraded to 2.4.2

As wrote in the title, after I’ve upgraded from Magento 2.4.1 to 2.4.2 the message “Only 0 Left” has suddenly appeared in the product page (configurable product).

I checked in Stores->Configuration->Catalog->Inventory->Stock Options->Only X left Threshold and it’s set to 0. I tried to set to -1 but nothing’s changed.

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Any solutions?