Yesterday, installation went well for the official WIN10 v1903 update. It took about 3 hours to download using “Update Assistant” and 1 hour to install

Below are a few early known issues from May 21 release

https://www.thewindowsclub.com/known-issues-with-windows-10-v1903-may-2019-update

https://www.windowscentral.com/windows-10-may-2019-update-common-problems-and-fixes

Windows 10 v1903 – May 21 2019 release