I am having this same issue – my WooCommerce database is up-to-date and I’m running the current version of the plugin (version 3.7.0). I have a product with six variations – variations 2 through 6 will not update to “in stock” even though I uncheck the “manage inventory” box and select “in stock” from the dropdown in the variation. I have also tried leaving the “manage inventory” box checked, increasing the inventory to “1” and saving, then unchecking “manage inventory” and saving again. These variations revert to “manage inventory” checked and “out of stock” every time.
