The whole Appreadiness service and black screen issue has been floating around for a couple of years now, but it's now raised its head again in WVD, at least where we're using FSLogix.
We have two WVD setups, one with FSLogix and one with no profile solution.
On the FSLogix one we're consistently getting black screens at login (although Ctrl+Alt+End works and you can run, say, notepad from Task Manager) but it eventually comes to life after five minutes.
In the event viewer the following error is associated with each black screen:
"A timeout (30000 milliseconds) was reached while waiting for a transaction response from the AppReadiness service."
Standard multi-user Windows 10 enterprise from the markteplace with is 1903 (although Windows itself is offering 1909 as an upgrade which I'm guessing is WVD supported, but I've not seen anything confirming this).
I've dug into this a little more. During the black screen, if I kill the App Readiness service then the black screen instantly disappears. Given that App Readiness should only run during the first log on of a new user, I think that it's kicking in before the FSLogix profile has fully mounted, i.e. : Windows 10 thinks it's a new user AppReadiness triggers Profile container fully mounts Appreadiness clashes with the now mounted profile.
Have you found any fixes for this. I'm running 1909 and have the same issues at the moment. If I disable AppReadiness the login process is pretty much instant. I don't understand why things can be running smoothly then all of a sudden this issue occurs.