The Fortran interface in HDF4 is broken on 64-bit systems since it stores pointers in 32-bit Fortran INTEGER values. If it’s working for you on a 64-bit system, that’s an accident.
Since there’s no funding to rework the interface, I’d like to remove it so people don’t use fundamentally broken code.
Perhaps someone in the community would be interested in creating a modern Fortran replacement. We could create a GitHub issue with pertinent information should someone like to do that.