Cannot add combination to cart even when it has stock

[iipa]

I came across a very mysterious problem. Let's say I have Product A, which has colors black and white. Black is default combination, and it's quantity is 0. White has 2 in stock. When I go to product A's page and try to select white, it shows that there are 2 in stock, but Buy-button is still disabled. I tried to reproduce this with creating new product, but I couldn't. For some products it works properly, but for some it keeps being disabled whatever I do.

What are the parameters that determine if combination is available for order? I have added my products through webservice, so I'm worried that there was an error somewhere in import.

I have debug mode enabled, and neither Presta or Apache logs or browser console show any errors.

Edited August 12, 2020 by iipa (see edit history)