Sean,
very interesting. Since 2010 (15 years ago 
) the SetupBuilder compiler can detect a .sbp project file renamed to a .sbi include script and then stop the compilation process with a fatal error. Your “load files.sbi” include script (created with SetupBuilder 6.9.2454) is such a renamed project file. But SetupBuilder (including the new 2025 BETA) can’t detect this one.
I’ll fix it in SetupBuilder 2025. Thank you for your help and for bringing this to my attention! I removed the “project” file specific properties from your “include” script and sent it via email.
Friedrich