My guess is that your movespeed was a really weird number with lots of decimals and the variance in number of moves the AoD got was due to which way the game engine rounded off the numbers. And depending on the attack speed of your Chainsaw, that might throw off those numbers even more, giving a wildly unpredictable movement pattern. Do you happen to remember your movespeed and attack speed?
I've outspeeded the AoD a few times and I've had that same experience. That's why, every time I try that strategy, I run a few laps around the Cathedral first to observe the AoD's movement patterns and see how long it takes for it to repeat. Sometimes, it goes a while before it does and then after I chainsaw it, it changes to a new movement pattern. Outspeeding the AoD is a strategy that needs a loooooot of patience. :)
tl;dr: I don't believe the AoD speed was changed. I think it's just wonky game engine effects.