The whole nitrite portion of a fishless cycle can be more dragged out than the ammonia portion. Often people come off "the spike" thinking that's going to be "about it" but then the A-Bacs keep producing lots of nitrite and the N-Bacs are just slower to develope fully into a population that can handle all that for sometimes quite a while after the spike phase. Don't lose heart, its a normal frustration we see a lot and time after time it eventually rights itself and the filter gets to working.
~~waterdrop~~