User may be unable to re-connect to disconnected session, unless the VDA is rebooted. 

You may see following events:

On the DDC you may see two errors Event ID 1039 and 1116 
1039 The Broker Service failed to contact virtual machine xxxx 
1116 The Citrix broker service failed to broker a connection for user xxx to resource VDA_name 

On VDA you may see following event:
1015 The Citrix desktop service's connection to the Citrix desktop delivery controller was terminated. 
Error details: Keep alive request was rejected. 

VDA was showing registered in Studio. 
This is intermittent and random to any VDA. User connected to dedicated VDA.

Following error is displayed to users when they attempt to reconnect:
Error:  ICA <VDA_name>  name resolution failed 

This issue occurs if you have Tanium security product installed
 

Workaround:
Remove KB4338818 from the VDA. Also remove KB4338823 if it is installed.

We recommend consulting Microsoft before removing the above Roll-up updates as they are security updates.

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Problem Cause

Issue is caused by Microsoft patch KB4338818 which conflicts with Tanium security product.
This issue is also caused when you have KB4338823 and KB4338818 installed