@johnsmith1 ProConnect does not store returns locally everything is stored on Intuit servers as the program is completely cloud based.  You also can't filter by ssn/ein in ProConnect as you can in ProSeries or Lacerte.  The search feature only searches by the return name.

Often times when a client return disappears, it is due to a change in Quickbooks Online Accountants for the rights to that client.  Please contact us at support.  We can have you invite us to the account to find it from the backend for you and get your access restored to the returns.  Any return that has been efiled can't be deleted from the ProConnect account so it would simply be hidden from your view based upon some change that was made to the client.