Scenario: You accidentally deleted your original persistent settings stream, which is why the Swarm nodes are reporting "Failed to read cluster persistent settings".
This stream is merely a text file with settings information and has nothing to do with the _administrators stream. Within the persistent settings stream is a setting called "domains", which contains a list of domains and the UUID of the domain stream. This is the list that is presented on the admin console and gets updated when a new domain is created.
If a new persistent settings stream is created after a domain already exists, the persistent settings stream does not know about that domain.
What we can do is add the domain into the persistent settings stream manually with an APPEND.
If you info the settings stream, you should see the line: domains=
Now when you read the persistent settings stream back, you should see the new "domains" line at the end of the file, but it may not have been picked up by the nodes yet. Reboot the nodes and the new domain setting will be picked up if this is the case.