I got logged out of Portfolio Administration when restoring a large backup. When I try to log back in, an "IdentitySeiUnavailable" error is displayed and then I am unable to log into Portfolio Administration.
Restoring large backups can take a bit of time. If you try to log in to Portfolio Administration before the backup is completely restored, you will get the "IdentitySeiUnavailable" error. Wait until the restore is complete, then you should be able to log in.