In Pro 2.0.1, when adding an AGOL HFS layer to a "New Map" via the Add Data icon, when right clicking on the layer in the TOC, selecting Properties, Metadata, all of the AGOL metadata is present (Title, Tags, Summary, Description, Credits, Use Limitations, Thumbnail).
In 2.1, same add data workflow, same AGOL source, when right-clicking on the layer in the TOC, select Properties, Metadata, only the title and the tags are populated. All other elements are blank, as is when you select "Edit" or "view" metadata from the right-click action.
This is pretty problematic, as I put a great deal of time into getting the AGOL metadata elements populated so the "Item Information" green line always reports "High". As I'm trying to use Pro to produce more downstream content (e.g Offline Map Package), having to re-create/re-edit all of the metadata doesn't seem very productive.
In trying to nail this down, I investigated (and discarded) number/length of tags, SQL reserved keywords, views hanging from the service, sync/edit settings....as the cause, this applies to all HFS's. So it appears something was introduced in 2.1 that worked in 2.0.1...