Then SetupDiag is your friend!
A new tool from Microsoft to run setup related diagnostics. It parses either online or offline all the relevant logfiles and extract the issue and mostly also shows how to fix them. Quicker you cant find the issue and the solution!
SetupDiag documentation and download (actually all you need)
https://docs.microsoft.com/en-us/windows/deployment/upgrade/setupdiag
General quick fixes for most common issues
https://docs.microsoft.com/en-us/windows/deployment/upgrade/quick-fixes
Here a good description how to read the error code if you want to
https://docs.microsoft.com/en-us/windows/deployment/upgrade/upgrade-error-codes
The full story of troubleshooting
https://docs.microsoft.com/en-us/windows/deployment/upgrade/resolve-windows-10-upgrade-errors
