Admin user logged out after restoring a snapshot in new hosting

Hi,
I am currently changing hosting, and I used snapshot pro to create a backup of my existing websites.
I have set up a fresh wordpress installation in the new hosting (siteground) and I proceded to connect WPMUDEV dashboard and install the snapshot plugin. The Wordpress admin user was different from the previous installation of the same website, and also the db table prefix was different.
I have uploaded the previous snapshot in the /wp-content/uploads/snapshots directory and discovered them in the snapshot tool, then I have restored it.
One website went thru smoothly, and the user to login was the same of the previous wordpress installation. Two further websites did not work well instead.
I entered the phpmyadmin interface, and I find out that in wpxx_usermeta (xx the additional prefix to the new DB table, while the previous was simply wp_) there were still two references to wp_capabilities and wp_user_level. I updated the two to wpxx_ , but still I receive an error message when I try to access the dashboard (it says the account does not have the authorization to access the page).
I checked the installation which went thru fine, and I saw the Snapshoot Pro tool automatically updated the wp_ prefix to wpxx_ also in usermeta table (which made me question why this didn't happen in the other two cases).
How can I fix the permission to get again my admin accounts to access the dashboard?
Thanks!
Luigi