Magento 2, category disappeared on "Catalog > Category" tree, does show everywhere else

Question

I have a Magento 2.2.2 build, I imported my products, categories and orders from a Magento 1.6.2 (don't blame me, I just got this) build using cart2cart

Everything looks to be fine, until I tried to add a new product sub-category

The new category shows fine, but all the old categories (only sub-categories under main category) disappeared.

the categories do show on the front end navbar

the categories do show on the back end product edit page, where you select what category the product belongs to

the categories do not show on the category edit page, in the category tree.

I have tried refreshing cache, reindexing and relogging my user, I have given it a day and Googled the problem... I have found nothing close to this, and am at a loss on where to look next.

I assume it would be something I may need to toggle in the database, though with the categories showing on the product edit page I am not sure what, but I do not know where to begin looking for that, and do not want to mess with the database without knowing all the interactions

1. I cannot delete the offending categories, because I can't access them on the edit page
2. I cannot recreate the categories, because it would not allow me to keep the url key that my existing site uses, meaning a hit on ranking, I am sure, among other things like anyone who links to a product would get affected, also the old categories would still show on the menu (cant remove without access) and on product creation, causing problems and confusion there

UPDATE 12/10 I have found somewhat of a workaround for this. I find the ID of the category in the database (catalog_category_entity_varchar.entity_id) searching by the name, getting the id, and then I replace the id in the admin url

1. go to manage categories
2. click on any category
3. replace the id in the url with the id of the item
4. make your change

that change will stick, but the item may (or may not) disappear again.. it seems to stick better if you change its parent category

Answer 1

I just had the same problem - when I checked Database i found that in category that disappeared in Table mggp_catalog_category_entity there is nothing in path field.

After writing path (copy from category that has the same category parent, and just change last number to your category entity_id) - after reindex, cleaning cache - ii starts to work,