Annoucement Article: Here

NOTE: Under Investigation: "Setup failed while installing the MSIs. A certificate chain could not be built to a trusted root authority".   It appears that the VM must have connection to the internet for the installer to work.

Changes include ( comments in Italics are my own):

Client Fix: "The Office Click2Run macro functionality does not work correctly with enterprise App-V virtualization." Recent changes to the Office Deployment Toolkit/Office365 packaging resulted in some macro (scripting) changes that required a client side fix in App-V to resolve.

Client Fix:  "The Office Outlook search functionality does not work correctly."

Client Fix:  "AppV Hotfix 7 fixed an issue in which a function of the Connection Group Optional feature was broken. After the hotfix was issued, we received reports that the PackageGroups registry hive consumes a lot of space in installations that involve App-V connection groups on RDS computers. A modified fix in the latest hotfix release significantly reduces the registry space that is used by the Connection Group Optional feature. It does this by grouping user settings based on the effective group that a user belongs to, instead of by individual users."

This fix likely also applies to both the RDS and the Windows Desktop clients, but only RDS client cared.  RDS clients using Citrix with PVS also don't care very much.

?Server? Fix: "When two or more packages in the same connection group have "Any Version" selected, and the connection group is upgraded at the same time, the packages are not published to the user.

I assume, but have not confirmed, that this is what the Server fix is for. But maybe it is in the client.

Client Fix: "A race condition exists between the App-V catalog manager and the profile roaming service. This condition is now fixed by a new registry key that controls the waiting period for the App-V catalog manager to allow any third-party profile roaming service to be completed."

Well they didn't specify which  third-party profile roaming service causes this issue. Possibly Appsense (now Ivanti) or may Citrix.  If you aren't using one  or aren't having an issue on some user logons, then you don't need to make the registry fix, documented below.  Basically, you are telling the App-V Client to wait after logon before doing any work with the catalog, allowing the third party product to finish it's work.  How long to wait? I have no idea.  Chances are your third party vendor support knows.

The registry key details are as follows:

This hotfix is a direct download of the components that you are interested in, including other MDOP components.  No email required on this one!

Note: Windows 10 version 1607 and above, and Server 2016 and above, clients do not install these hotfixes as standalone installers any more.  The fixes would be applied to, and delivered by, operating system updates delivered via normal channels (e.g. "Windows Update").  Microsoft tells us that fixes should generally appear first in the 10/2016 branches before releasing the 5.1 branch; The client fix appears to be covered in the March non-security updates, while the sequencer fix would require a Microsoft Support Case (charges might apply?)  

NOTE:  App-V Hotfixes always include prior fixes on the same release.  In other words, you only need to apply the latest hotfix (5.1 HF9 in this case) and it includes other prior hotfices (5.1 HF1 through HF8 in this case).