After upgrading to 1903 on multiple PCs and VMs, there is an odd issue with RDP that is different from the infamous "black screen" RDP issue. In my case, the target is a VM on a Windows 10 Hyper-V host. RDP works perfectly fine on the initial connection, but if the RDP session is disconnected, trying to reconnect shows either a black screen, a white screen, or a frozen "logging on" screen. The target VM becomes completely unresponsive. Even the console Connect option in Hyper-V Manager is unable to connect to the VM. I have to forcibly power down the VM and start it up again. If I continue trying to connect with RDP, the VM will blue-screen and restart.
The graphics driver solutions for the black screen issue do not apply here because it's a VM, not a physical PC. Update KB4512941, which addresses the black screen issue, did not fix my issue. The solution/workaround to disable WDDM on the target VM does fix the issue, but I certainly would prefer an actual resolution so that I can re-enable the superior WDDM protocol.