Users are unable to log into XenApp servers. Sessions freeze and users getting stuck. 
There are logs related to the Citrix- Multimedia - Rave/Admin 
 that "HDX Mediastream failed to establish mediastream connection." 

Issue 1

• Dump ec01mortvdi01_memory.dmp shows several sessions lingering in disconnected state. 
• All the session have the same issue where winlogon.exe is waiting for an ALPC reply. 
• The ALPC wait chain goes long way from process.
• Winlogon.exe  svchost.exe -k GPSvcGroup  CitrixCseEngine.exe lsm.exe
• Process lsm.exe is waiting to acquire a global resource. 

Solution 1

• The first issue looks like a known issue of CitrixCSeEngine. 
• Refer to Microsoft hotfix: An application or service that uses Winsock API or Winsock Kernel API may randomly stop responding in Windows Server 2008 R2 or in Windows 7.

Issue 2

• Dump EC01BranchVDI03-Memory.6.2.15.dmp shows four threads spiking on user mode for more than 30 mins.
• All thread belong to Wmiprvse.exe. 
• The stack of all these threads is empty. 

Solution 2

• Refer to Microsoft hotfix: You find high CPU usage for the Wmiprvse.exe process on a terminal server that is running Windows Server 2008 when you run the Windows System Resource Manager