Well, that’s the thing, I can partially do so in the UI.
- Creating a new group works
- Pre-existing groups from 2.1 are breaking with regards to LCE and CV/CS.
Did some schema/db conversion go haywire? I know my way around Foreman/Katello, but this goes a bit deeper than I know 
I dug up some info from the DB (this is all from a lab VM):
From the hostgroups table in Katello 3.16:
id,name,created_at,updated_at,environment_id,operatingsystem_id,architecture_id,medium_id,ptable_id,root_pass,puppet_ca_proxy_id,use_image,image_file,ancestry,vm_defaults,subnet_id,domain_id,puppet_proxy_id,title,realm_id,compute_profile_id,content_source_id,grub_pass,content_view_id,lifecycle_environment_id,lookup_value_matcher,kickstart_repository_id,subnet6_id,pxe_loader,description,compute_resource_id
11,CentOS7-Base-Acceptatie,2020-11-20 19:39:32.886917,2020-11-21 10:12:18.656595,,2,1,,136,$6$xxxxx.,,,,,,4,4,,CentOS7-Base-Acceptatie,,,1,$6$xxxxx,15,6,hostgroup=CentOS7-Base-Acceptatie,147,,PXELinux BIOS,"Managed by Ansible, your changes will be lost",
Same group and the newly created “test” group, Katello 3.17:
id,name,created_at,updated_at,environment_id,operatingsystem_id,architecture_id,medium_id,ptable_id,root_pass,puppet_ca_proxy_id,use_image,image_file,ancestry,vm_defaults,subnet_id,domain_id,puppet_proxy_id,title,realm_id,compute_profile_id,grub_pass,lookup_value_matcher,subnet6_id,pxe_loader,description,compute_resource_id
11,CentOS7-Base-Acceptatie,2020-11-20 19:39:32.886917,2020-11-21 10:12:18.656595,,2,1,,136,$6$xxx.,,,,,,4,4,,CentOS7-Base-Acceptatie,,,$6$xxx,hostgroup=CentOS7-Base-Acceptatie,,PXELinux BIOS,"Managed by Ansible, your changes will be lost",
36,test,2020-11-23 23:12:08.968592,2020-11-23 23:25:33.09145,,2,1,,136,"",,,,,,,,,test,,,"",hostgroup=test,,PXELinux BIOS,"",
katello_hostgroup_content_facets table (complete table, just has 1 line, which might have to do with the fact I created a complete new group that did work)
id,hostgroup_id,kickstart_repository_id,content_source_id,content_view_id,lifecycle_environment_id
1,36,147,1,15,6