Update:

I've only managed to scan one of the rolls of FP4 I processed most recently. From what I can tell, there are no marks of uneven development anywhere, so that's a plus. On the other hand, I am still dealing with water splotches on my negatives after the initial air dry (no chamois or squeegee). Are you guys sure reverse osmosis water is fine? That's the only thing I can think of. I made sure I had exactly 1L of it and 5mL of Ilfotol (even made sure the Ilfotol wasn't it's usual bubbley-ness).