Windows – Slow Initial RDP Connection to Windows 10

Since upgrading a machine from Windows 8.1 Professional to Windows 10 Professional (workgroup, no domain membership), I've been experiencing a rather strange issue that I can't figure out. The initial remote desktop connection is very slow to connect (on the order of two minutes). However, after the initial connection is made, I can close the connection and reconnect almost immediately. Also, after the initial connection is made, I can close the connection and reconnect using another machine entirely without experiencing the long delay. I've tested the remote desktop clients on Windows 7, 8.1, and 10, and all experience the same slow initial connection to the Windows 10 machine, so I believe the problem lies on the server side.

Things I've tried so far:

• Turning off "Automatic Root Certificates Update" via local computer policy:
  (Computer Configuration -> Administrative Templates -> System -> Internet Communication Settings -> Turn Off Automatic Root Certificates Update).
  Suggestion from technet, by user "dsoic" midway down the page. It was also suggested to disable CredSSP, but I don't think disabling Network Level Authentication is a good choice.
• Forcing TCP as the only RDP transport protocol
  (Computer Configuration -> Administrative Templates -> Windows Components -> Remote Desktop Services -> Remote Desktop Session Host -> Connections -> Select RDP transport protocols),
  suggested by user "Jayson Allen" on spiceworks. I also checked the FIPS setting, but on Windows 10 it appears to be disabled by default.

Neither has improved the situation. Does anyone have any advice on how to proceed?

EDIT: The Threshold 2 update has corrected this issue on my system.