Your second post started to ring some bells for me. I think it might be related to this:
TL;DR: loading can not be done dynamically, Defold automatically scans for string paths when building/bundling.
I wonder if we could confirm this is the case by first doing a dummy load using a hardcoded string, and then do it again using a variable? If my theory is correct then that should work. You’ll need to redesign if so, but at least you’ll know “why”.