It’s come to my attention that there’s a showstopping issue in Katello 3.18.0 for those using Pulp3 [1]. If you’ve installed Katello freshly from 3.15.0 or above, you’re using pulp3. The issue is explained in detail here on the forum[2]. If you are using pulp3 then you should not yet upgrade to Katello 3.18.0 because your content hosts will no longer see the content which they are subscribed to. This issue will be fixed in the upcoming Foreman 2.3.2 (because it’s a change to the installer, not Katello itself) release. I’ll ensure this thread is updated when upgrading is safe for pulp3 users.
[1] Bug #31548: Incorrect legacy dir in Pulpcore migration - Installer - Foreman
[2] Updating Foreman 2.2.1 to 2.3.1 and Katello 3.17.1 to 3.18 issue