My configuration

All servers - Windows 2012 R2.

One Connection Broker. Two collections with several RD Session Host servers. One Web Access server.

There is policy for RD Session hosts:

Restrict Remote Desktop Services users to a single Remote Desktop Services session: Enable

But from different RD clients I can launch two sessions on different RD session host servers from the same RD collection.

How to disable multiple remote desktop sessions per user per RD collection?

Hi,

I suggest you run GPresult.exe on terminal servers to check whether the group policy setting is applied correctly.

Gpresult

https://technet.microsoft.com/en-us/library/cc733160.aspx

If the policy setting is applied, please check RD Connection Broker related logs to find out why the Connection Broker failed to find/redirect users to existing session. Logs can be found under Event Viewer -> Applications and Services Logs\ Microsoft\ Windows\.

Best Regards,                   

Amy

Policy is applied successfully on all RD session hosts.

And I think that policy works correctly. Because there is no more than one user's session on the same RD session host server. User has sessions on different RD servers.

Moreover, I see in logs that connection broker finds existing user's session but creates a new one:

rduser connects for the first time and is redirected to the server RD2:
RD Connection Broker received connection request for user MYDOMAIN\rduser. 
Hints in the RDP file (TSV URL) = tsv://MS Terminal Services Plugin.1.RD 
Initial Application = NULL 
Call came from Redirector Server = RD1.MYDOMAIN.com 
Redirector is configured as Farm member

RD Connection Broker successfully processed the connection request for user MYDOMAIN\rduser. Redirection info: 
Target Name = RD2 
Target IP Address = 192.168.253.151 
Target Netbios = RD2 
Target FQDN = RD2.MYDOMAIN.com 
Disconnected Session Found = 0x0

This connection request has resulted in a successful session logon (User successfully logged on to the end point). Remote Desktop Connection Broker will stop monitoring this connection request.

Session for user MYDOMAIN\rduser successfully added to RD Connection Broker's database. 
Target Name = RD2.MYDOMAIN.com 
Session ID = 72 
Farm Name = RD

rduser connects from another machine:
RD Connection Broker received connection request for user MYDOMAIN\rduser. 
Hints in the RDP file (TSV URL) = tsv://MS Terminal Services Plugin.1.RD 
Initial Application = NULL 
Call came from Redirector Server = RD1.MYDOMAIN.com 
Redirector is configured as Farm member

Connection broker finds existing session:
RD Connection Broker successfully processed the connection request for user MYDOMAIN\rduser. Redirection info: 
Target Name = RD2 
Target IP Address = 192.168.253.151 
Target Netbios = RD2 
Target FQDN = RD2.MYDOMAIN.com 
Disconnected Session Found = 0x1

But Connection broker redirects user to another server RD1 with another session ID:
Session for user MYDOMAIN\rduser successfully added to RD Connection Broker's database. 
Target Name = RD1.MYDOMAIN.com 
Session ID = 75 
Farm Name = RD

Hi,

RD Connection Broker successfully processed the connection request for user MYDOMAIN\rduser. Redirection info: 
Target Name = RD2 

But Connection broker redirects user to another server RD1 with another session ID:

The redirection behavior seems pretty contradict to me.

Please fully patch terminal servers to see whether the issue persists.

Best Regards,

Amy

All of my RD servers are fully patched.

I noticed that problem exists only for users who connects from Mac OS client.

BTW, I use RDP security layer

Hi,

I noticed that problem exists only for users who connects from Mac OS client

Please try to download the new Microsoft Remote Desktop Preview app for Mac to see whether the issue persists.

Introducing the new Microsoft Remote Desktop Preview app for Mac

http://blogs.msdn.com/b/rds/archive/2015/08/11/introducing-the-new-microsoft-remote-desktop-preview-app-for-mac.aspx

Best Regards,

Amy