Here's another glitch. It happened to me after "feature"-updating the W10 OS from version 1803 to 1903 - RDP would not connect properly (or not at all with repeated tries after the first failure). The RDP window was completely black. After much web searching, I found this pretty specific clue:

"Installing 1903 (WIN 10) on an older PC with certain chipsets resulted in a black screen while using RDP. This is a known issue, discussed by Microsoft as late as July 12th [2019] and still awaiting the fix (promised for July-August). The black screen issue has to do with a new display driver (WDDM) used in 1903. The “fix” forces the old XDDM driver to be used.

"Easy fix! Use GPO to force use of XDDM rather than WDDM. In Group Policy Editor under Remote Desktop Session Host -> Remote Session Environment ... set the policy “Use WDDM graphics display driver for Remote Desktop Connections” to DISABLED." From <https://www.tenforums.com/network-sh...ne-1809-a.html>

Interestingly, this fix didn't actually seem to work! So in addition to the policy change, I updated the Intel HD Graphics driver on my observatory computer - a model that is several years old, and one (probably) that is susceptible to this problem, i.e. having a "certain chipset."

Updating the graphics driver worked - at least the first try to connect was successful. Subsequent tries were sketchy, some failing as before. I also discarded the saved credentials in the RDP client application, and rebuilt and saved them anew. However this again ultimately failed.

There was also noted a Microsoft KB fix for this, KB4512941, that might have taken care of this problem, but I didn't not apply it. Instead, I updated the OS with the 2019-10 Cumulative Update package which presumably includes that KB.

Having done these two updates, driver and OS, I rebooted the computer several times. Somewhere along this process, the problem seems to have gone away. I've been able to connect via RDP multiple times without again seeing the black screen. Ultimately, I'm not sure if it was just one or a combination of these changes that eliminated the problem. When you make three or four changes at a time, it's never possible to find the culprit.

For others having this problem, there's lots of "literature" available on the Internet.