You get the message "Check and correct the level_depth field" from the menu Catalog > Tools to edit your categories (id_category:819)" when performing a CSV export.
There are a couple of solutions:
For the latter, you then need to look into the database tables in order to identify the category (by phpMyAdmin for instance):
Create a new entry in the table ps_category with the id_category = 819 ; id_parent = 1; position = 999
You will find the category at the root of your website
Delete data related to id_category 819 in the table ps_category
Look into ps_category if id_parent 819 exists: if it does exist, then replace the value id_parent 819 by id_parent 1: you will find this category at the root of your website.
Delete data related to id_category 819 in ps_category_shop
Also note that Sc FixMyPrestashop verifies the integrity of all categories tables of your database, directly from Store Commander's interface, and also fixes any errors found, all in just a few seconds.