New projects seem to have random "Feature Visibility" settings
In the past few days I've created a handful of new projects on gitlab.com. While the group and all the projects were set to "Public", unauthenticated users could not browse the repository and/or registry on some projects, but they could on others. I went into the project settings and noticed that some features were set to "Only team members" and others were set to "Everyone with access". There did not seem to be a pattern. Changing the settings to "Everyone with access" restored the ability for unauthenticated users to view the repos.
Prior to discovering this, I did not change any of the default project settings. They were either created with different defaults or some other action caused the permissions to change in an unanticipated way.