After Gmail migration: folders are not shown in sidebar

Hi,

I've just successfully migrated emails from two gmail accounts to my new account at Zoho.
There is one problem with folders, though: folders were imported, but they don't appear in the sidebar, nor can I select these folders in the search.

I know that the folders exist, because the folder name is displayed when I view the list of emails.
Only two of the custom folders (labels on Gmail) were imported correctly, i.e. only these two folders can be selected.

How can I fix this?