I had this problem for years. After a lot of research and experimentation, I created the following script and it works for me and some of my colleagues...
Put the following in a text file and name it as .bat (like Release_RD.bat)
tasklist -s your_machine_name -fi "imagename eq mpnotify.exe"
set /p pid=Enter PID found above:
taskkill -s your_machine_name -pid %pid%
pause
If you aren't currently looking at the spinning Welcome screen, attempt to log in again so that your remote desktop client is actively on the Welcome screen
Double-click the .bat script and follow the directions in it. You might have to run the script twice if there are multiple mpnotify.exe processes.
If it works, the hung remote session will then proceed past the Welcome screen and you'll be logged in.