qulfontcompiler is called using a command line generated by the host tool in build steps.
However, the length of the command line increases depending on the number of text and font files on the source files that your application uses.
If that length exceeds the OS limit, calling qulfontcompiler will fail and qul_font_engines.cpp is not generated.
compile error is here:

[ 18%] Generating CMakeFiles/XXX.dir/qul_font_engines.cpp, CMakeFiles/XXX.dir/qul_font_data.cpp
jom: C:\work\build_directory\XXX\CMakeFiles\XXX.dir\build.make [XXX\CMakeFiles\XXX.dir\qul_font_engines.cpp] Error 2
jom: C:\work\build-directory\CMakeFiles\Makefile2 [XXX\CMakeFiles\XXX.dir\all] Error 2
jom: C:\work\build-directory\Makefile [all] Error 2
15:29:11: The process "C:\Qt\Tools\CMake_64\bin\cmake.exe" exited with code 2.
Error while building/deploying project XXX

workarounds:

change the build directory to short path.

qulfontcompiler is failed by the command line length is oversized OS limitation. So that it can take work around this by by changing the absolute path of the build directory to a shorter path.