In a newly created nexus 3 repo, I was busy adding proxy repositories. After discovering I made a typo in the name, I selected ‘delete repository’ to remove and recreate it. That did not work. Then I kept getting a red ‘illegal status DELETED, expected STARTED’ popup. New repositories added after were not shown, but present, because the name was said to be ‘in use’. After a restart the whole repository list is empty.
This sounds like something that would be best handled over a Jira issue. Please raise one at https://issues.sonatype.org in the “dev - nexus” project.