When attempting to migrate a list, one of the following messages is displayed:
Could not add the content type to destination list. Validate that the site columns used by the content type aren't corrupted.
Could not add a field to the destination list, because the associated site column is corrupted.
Sharegate was unable to add a content type or a column on the destination list, which will result in missing columns in the destination list (when compared to the source list).
This problem normally occurs because the list uses a site column that is corrupted in the destination site, or because the list uses a content type that refers to a corrupted site column.
To validate that the cause really is a corrupted column in the content type, you can try to manually add the content type to the destination list and see if you get an error. If you do get an error, try manually adding each site column used by the content type to your destination list until you get an error. Once you find the one that is failing, you can simply delete the site column from your destination site and migrate it again from your source site (to make sure it is not corrupted any more). Make sure to add the new site column to the content type after you migrate it.
To validate that the column really is corrupted, try manually adding the site column to your destination list. If it fails, it means that the column is corrupted. You can then simply delete the site column from your destination site and migrate it again from your source site (to make sure it is not corrupted any more).