RDP Bug in Win10 v1903 - disconnecting RDP sessions WITHOUT LOGGING OFF causes one CPU core to spike
As a workaround on all of my affected machines I have used Group Policy Editor to set
Local Computer Policy - Computer Configuration - Administrative Templates - Windows Components - Remote Desktop Service - Remote Desktop Session Host - Remote Session Environment
-> Use WDDM graphics display driver for Remote Desktop Connections to DISABLED
This forces RDP to use the old (and now deprecated XDDM drivers)
After rebooting, behaviour returns to normal and after disconnecting from an RDP session the RDP host (target machine) no longer shows DWM.EXE consuming CPU.

To my knowledge, this problem is not yet confirmed by Microsoft, although anyone can reproduce it on any hardware and any VM.

https://answers.microsoft.com/en-us/windows/forum/windows_10-performance/after-exiting-a-remote-desktop-session-cpu-load/e21e7da0-9a64-4a14-a671-b7cb1b61f66e?auth=1&page=1 proves, that this problem is common (more than 10,000 people indicated that they have the same problem!)

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