I had a lot of difficulty installing the Windows 10 April Update (version 1803). I tried to install it a few times with no success last night. I tried the Microsoft Windows 10 Media Creation Tool, which was was a total flop. I tried turning off the firewall which did nothing, restarting after each attempt, ran the Windows Update troubleshooter and got nowhere.
I just kept trying to get it to install from the Windows Update window on my laptop. All totalled, I probably tried 12 times. I even got up at 1 AM to check on the install and it was unsuccessful again. I gave it one more try and went back to bed. Surprisingly this morning I found that it actually installed when I saw a window on my screen that said the Welcome to Windows 10 April Update!
I don't know if it was persistence or what. It was very frustrating. I'm glad I was finally patient enough with it to just let it do it's thing.