I am having simular issues and just found this comment on --> Comments | VMware Flings :
"We discussed this today and this is probably related to another setting. The Welcome screen is displayed for the amount of time allowed by this timer.
The issue is described in this MS article (it also applies to Windows 10 even though it only mentions Vista and Server 2008)
If we leave this at a high value, then logons will always take at least that amount of time. E.g. If the timer is set to 30 seconds, even if all processing has been done in 10 seconds and the desktop is really ready, the user wouldn't get access until at least the 30 second count.
We want the delay to be a short as possible so that the session is switched from logon to the other processes that happen at logon. The downside is that the Welcome screen is only displayed during the logon session and a black screen is then displayed when other processing is happening. The duration of the other processes and therefore the black screen can be affected by things like antivirus processing, GPO, App Volumes mounting operations, etc."
I hope this is usefull for your issues!
That was correct, updated that key in the optimization tool to update to 30 and it adds about 30 seconds of welcome to the logon instead of black screen. Looks like without the key it is about 60 - 70 seconds. Next step will be to see how much we can reduce that but this will allow us to push our progress to prod this month. Thanks again