The display of out of stock products is enabled in the store configuration. This means that out of stock simple products are displayed. But if one or more configuration of a configurable product is out of stock then the swatch of that product is missing from the swatch list of that product.
How do I make all swatches visible, even for out of stock configurations?
There have been a number of questions and answers in this topic but none of them work. Particularly the one that recommends to set Use configuration options under the products' Advanced inventory. This option is not even there in M2.2.7. Another solution involves a custom module but according to comments some files are missing.
The solution posted here is no help either because stock is refreshed from our remote server via Magento 2's API multiple times a day, so setting a stock manually for these simple products would be pointless.
So please do not mark this as a duplicate.
Thanks in advance for all the help!