A recent support thread revealed that somehow an OS can get an incorrect title:

#<Redhat id: 2, major: "8", name: "CentOS", minor: "1.1911", nameindicator: nil, created_at: "2020-06-06 02:50:37", updated_at: "2020-06-06 02:50:37", release_name: "", type: "Redhat", description: "CentOS 8", password_hash: "SHA256", title: "CentOS 8">

Notice that the title should be 'CentOS 8.1.1911'. I instructed the user to just 'Submit' the form for that OS and the before-save hook fixed the title. https://community.theforeman.org/t/subscription-manager-register-error-in-katello-3-15-3-1/19625

IMO this warrants an investigation into how they could get into this state