Foma films build up contrast far faster than any other make they need about 75% less development (time) to achieve similar tonality and about half the film speed. I've been using them for about 5-6 years with no issues like this, but Rodinal contains hydroxide so I'd use a good plain water rinse not a stop bath. Don't shake up developers, fixers etc before mixing as that can take particles settled on the bottom of a bottle into the working solution, Foma films are softer and they can lodge on the surface of the film. Ian