This issue impacts only users with a Teacher role in Moodle.
A bug in Moodle 3.11 is causing some course restores to fail with the error message: error/moodle/setting invalid ui label. This occurs when the course that was backed up has unnamed topics. Moodle is working on a fix for later upgrades, but the workaround is to add placeholder text to name field for all blank topics in the course you are backing up, then recreate the backup. This new backup should restore correctly, and you can remove the placeholder names you added after the restore is complete if desired.
If this workaround doesn't work or you have questions or need help with Course Backup and Restore, please contact the Help Desk (firstname.lastname@example.org or 610-526-7440) and they will alert the Moodle team.