The only thing I can relate to your issue is I had an aponogeton bulb that I sprouted and grew in my bowfront. No ferts to speak of, lighting is sub par, but it grew like wild for several months, then all of a sudden it quit growing. I chalked it up to that it maybe exhausted the nutrients in the water or whatever, but then I moved it to a heavily planted tank that was running co2 and regular ferts, everything growing like mad, and it never did. It stayed alive, but didn't do anything, so I blame that one on the plant itself. As far as that happening with multiple plants, I'd lean more towards a fert/light/water issue