Your black spots might be related to “pepper fogging”. This is reportedly more often seen in the development of lith films and in lith printing, aerographic films, but might also be seen in regular films as well. I also found a reference to it happening with the now obsolete Kodak HIE film, but I suppose it could happen with any film under the right circumstances.
It’s related to the process, not the film. The developer might be a suspect.