Hi there,
Recently, I was working on a Windows server 2012 R2 upgrade to Windows server 2019. Some of the servers failed to upgrade after 51% with an error message - "The Installation failed in the FIRST_BOOT phase with an error during SYSPREP operation"
The log file(setupact.log) will be accessible from C:\ drive. you will able to find it under a hidden folder - $WINDOWS.~BT
Remove-WindowsFeature -Name RDS-Web-Access
After removing the rds-web-access feature, the upgrade was completed successfully.
Note: You might have to reconfigure the RD-web page or restore from the old backup. (Please comment if you found any alternative option to restore the web form.)
#> echo "Thank you :)"