unfortunately yes a lot of times 
sca is enable for me and i think it is the reason why but i saw in katello that the sca enable option is set
i saw an old post with a similar issue (exept for me after upgrading pulp from 2 to 3 it worked fine)
my issue appears suddenly at the end of september or begin of october
i can run this command like in the post (Unable to sync repositories after ContentMigration to pulp3)
[root@katello ~]# foreman-rake console
Loading production environment (Rails 6.0.3.4)
irb(main):001:0>
irb(main):002:0>
irb(main):003:0>
irb(main):004:0>
irb(main):005:0>
irb(main):006:0> ::Katello::Repository.find_by(remote_href: '/pulp/api/v3/remotes/rpm/rpm/f65c385a-78fb-4970-a9c7-38adddfc60c9/')
=> #<Katello::Repository id: 252, pulp_id: "d28d7e44-91ed-490f-a0b1-a2cf8a134775", library_instance_id: nil, content_view_version_id: 1, relative_path: "SPB/Library/custom/RedHat_repositories/RHEL_8_Apps...", environment_id: 1, saved_checksum_type: nil, distribution_version: nil, distribution_arch: nil, distribution_bootable: nil, distribution_family: nil, distribution_variant: nil, container_repository_name: nil, root_id: 46, remote_href: "/pulp/api/v3/remotes/rpm/rpm/f65c385a-78fb-4970-a9...", publication_href: "/pulp/api/v3/publications/rpm/rpm/51e5d20b-e3d2-43...", version_href: "/pulp/api/v3/repositories/rpm/rpm/9ebf4539-082e-46...">
thanks a lot
ludo