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VDA Unregistered Session Prepare Failure


Hi folks,


We recently rolled out a new farm.  CVAD 1912 CU2 VDA's using PVS.  The server OS is server 2019 datacenter.  These VDA's primarily server out Seamless Apps.


We have been experiencing an issue, where the VDA's would randomly go to an Unregistered state.  Looking at Director, it would state "Session Prepare Failure" and occasionally "Contact Lost".  This was happening multiple times per day on a Delivery group with 7 VDA's.  We updated to CU5 and the problem has reduced, but still occurs two one or two of the machines once per day now.  The specific VDA is random. 


This has had a significant impact on users.  When this occurs, those user sessions that were on the affected VDA are now hung, and the users cannot reconnect to get a new session.  In Hyper-V looking at the VM, if you connect, it is just a Solid Blue Windows background.  No Ctrl+Alt+Del.  Nothing.  Just a background.  To be clear it is not a BSOD.  The only way to correct the issue is to reboot.  Typically I have no problem using the reboot option from Director.  It does reboot the server just fine.  Once done the sessions are removed and users can now establish a new connection.


I have spent a couple of days looking through Articles, Event Logs, etc.  But none appear to be my issue, or have I found any useful events that would elude to the problem. Although I have found similar situations, nothing that is quite like what we are experiencing.  We do not use Shadowing typically.  Although it is enabled, there are only 2 of us that have access to do so and we have never used on this new farm.


I would appreciate any advice or support!

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We upgraded to the latest CU.  And I have resorted to nightly reboots of the workers.  This only happens on one of our farms.  The other farm, the workers will last for 6-7 days before this occurs so we just reboot on the weekends.  Otherwise, for the farm that experiences this, the nightly reboot keeps the problem away 95% of the time.  There is still the occasional unregistered worker during the day unfortunately.

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