Bad fixer would give you normal negatives with a grey veiling over them, and a milky appearance where they should be clear.(posted 8244 days ago)
The Ilfosol-s has oxidised and gone bad, simple as that. Some developers just don't keep very long once they're opened.
March to November? Hmm, let's see, that's twice as long as Ilford recommends, so what do you expect? Didn't the slightly brown colour tell you something?