I recently faced this strange issue at one of my clients WordPress eCommerce site, its categories were vanished from the product edit page
However in the WordPress dashboard, under “WooCommerce Right Now” section category count showed up just fine.
WooCommerce stats .. it still showed the category number (ex: 15 categories etc.), I checked and re-checked and couldn’t figure any issues with the site/installation of plugin files.
Also when I visited some of the existing category pages, they showed .. nothing found message:
Finally after Google‘ing for couple of hours and digging into the issue … I found out that my themes and plugins and WP installation is just fine, its probably the server, the after contacting the support team, they confirmed that the servers /tmp was full and that was causing the issues we were facing on the site and after they cleaned the /tmp directory and set it on auto .. the issues were fixed and so far .. never happened again.
Hopefully this article will help some other poor soul out there of some extra work.