The Cat1 tickets are only visible to those who were registered for the ballot but unsuccessful.
If you didn't enter the ballot you can only see the 'prime' seats at the moment - Any Cat 1 etc tickets will become available at a later date for general sale if not picked up by those who were unsuccessful in the ballot.
Thats why some can see them on the Uefa site and others can't
The Cat 1 (or Cat 2) tickets that come up will be resale tickets - probably returned by those from other clubs that were successful in the ballot but now not going as their team isn't involved.