I suspect that what you are Importing is sessions for which Protection has expired
Every day at Noon, a Maintenance runs, part of which is to remove the Catalogs from Expired sessions. It is important to IMMEDIATELY go to the Internal Database, find the Imported session, and reset the Data Protection. Catalog Protection, by default is the same as Data Protection, but, feel free to reset this also
Try to avoid Importing at any time close to Noon
I also advise that you not use Interval when trying to Restore. Set your Search Interval to None. When you have selected what you want to Restore, right click on it, and, from the drop down, select 'Restore Version', to get thebackup version that you want to REstore from
