I'm having the same problem with my IPA. Thought the yeast was dead, so I went to repitch but the fermentation started up (this was after a 3-4 day lag). I think the oxygen thing is probably a major player, maybe there just wasn't enough after it was sitting there for that long... also I have a feeling my pitching temp was WAY lower than my thermometer was telling me. I bought a new one and was shocked to see how low it was after the lag time. Regardless, the hydro sample I just tested tasted really good. Still cloudy as hell, so maybe it's still going down, but very tasty and I couldn't really detect any off flavors.