These are corrected and known problems with upgrades to 2004:
Resolved issues in Windows 10, version 2004 and Windows Server, version 2004 - Windows Release Information
Windows 10, version 2004 and Windows Server, version 2004 - Windows Release Information
New problems can be reported using the Microsoft feedback hub:
https://support.microsoft.com/en-us/help/4021566/windows-10-send-feedback-to-microsoft-with-feedback-hub-app
There is a default 10 day rollback period.
The 10 day default period can be modified.
