No, that I’m sure it could not happen. fpm knows nothing about where the source files are for the included library, it just includes the precompiled .mod files since I feed them as compiler flags, via pkg-config. Also, the very same behavior (compiling and running correctly before, now failing after adding external to implicit none) happens using the Makefile, too (and the Makefile adds every obj one by one).
EDIT: I mean, I could even delete the library source files and everything would happen regardless, since I’m checking out a completely independent repository, and linking the library relying on pkg-config only.