Non admin users are getting "Security constraints prevent access to requested page" while the upgrade was running and shortly after the upgrade monitor populated Xanadu upgrade was completed.Issue Symptoms: Non admin users are getting "Security constraints prevent access to requested page" when they try to navigate to any page while the upgrade was running and shortly after the upgrade monitor populated Xanadu upgrade was completed. Business Impact: Non-admin users are not able to work on the instance while the upgrade is in progress. Root Cause of the Issue: This issue was caused by sys_security_acl_5ac4bb13931102009c8579b4f47ffba2 being customised and empty. It has been observed that this ACL was customized and did not receive updates from the Vancouver release. Prior to the Xanadu upgrade, it was empty and lacked configuration items. Please note that in Vancouver, our Dev team added minimum Security Attribute configuration to ACLs to prevent resources from being overly permissive. However, since this particular ACL was customized, the changes were not applied to the instance and were skipped during the upgrade to Vancouver. Solution Provided: To avoid potential temporary outage issues during the production upgrade, we recommend fixing any empty ACLs before proceeding with the upgrade to Xanadu. Preventative Measures: We have introduced a new backend security feature - "empty ACL bouncer" which runs (hourly) background scan and patch job to ensure there are no empty ACLs in the system. After the upgrade monitor indicates that the process is complete, non-Admin users should be able to log in to the production environment approximately 20 minutes later, once the upgrade change has fully completed.