This article applies as of PRTG 22
Monitoring Citrix XenApp servers without disconnects
PRTG does not directly cause problems in Citrix environments. The disconnects of XenApp terminal servers are the result of an error in the Citrix service that appears after the logoff of an RDP session.
In this case, the affected server changes to the status unregistered for a few seconds. If you monitor the server with the RDP (Remote Desktop) sensor, this status change happens with every sensor scan.
You can resolve this issue with the Citrix private hotfix LC0251 that is specific to these RDP session disconnects. Apply this fix to your Citrix XenApp servers and the problem will not appear anymore if you monitor the Citrix environment with the RDP (Remote Desktop) sensor.