Duplicate of BUG-000126821: This issue was addressed along with BUG-000126821.
Both of the issues are related to upgrading to an ArcGIS 10.6 or later geodatabase which involves recreating EVW geodatabase system views. This bug can cause the upgrade to fail if the user performing the upgrade is a member of the db_owner role, but not the owner of the EVW view. Upgrading the geodatabase when connected as the DBO user may succeed but permissions previously granted to the EVW view are not granted again during the upgrade process.