When I try to build the installer on Windows from the command line it returns to the prompt immediately but no error message is shown

This is due to builder.exe being compiled as a GUI application and not a console application, so it returns inmediately and does not output to stdout. Starting with 6.0 there is also a console build called builder-cli.exe that does not have this proble,

In case you'd like to receive some feedback from the console to know when the building process is finished, you could create a bat file that in turns executes the builder.exe application. That will block until the build is completed.

Optionally, you can also redirect to a log file the stdout:

"C:\Program Files\BitRock InstallBuilder for Windows 5.4.2\bin\builder.exe" build "c:\Users\user\Documents\InstallBuilder\projects\demo.xml" > log.txt