@Christoph-Hart Thanks, yest that's the first thing I checked...
I re-created another minimal snippet from a new project (the previous one was the main project that I stripped down until having nothing, so I might have carried on a problematic setting of some sort.
This new one (identical snippet with just a simple ScriptFX) works and runs fine. I did copied the preprocessors from main project and that minimal snippet it's still working. So there might be a setting or a corrupted file. I remove the Binary folder entirely at each iteration to be sure it's clean.
I'll try a diff between the two "identical" minimal snippets to see why one is not working...






