I have had exactly the same experience. It is what happens in my opinion when you start to progress to the ultimate of CrossFit - The rx'd group!
I found that as my times improved i was having to up the weight closer to 'as prescribed' and my times were taking a beating.
Keep unleashing the inner dawg and you'll keep on rocking!
By the way 'Helen' is my favourite 'girl' and i've now erm.......done her :uhoh: 3 times, each time as rx'd and steadily improved............it will happen and you will blow it out of the water soon, i have faith.
So i guess i'm saying.....don't worry about the time so much. As soon as you get it close to the monster's times (Kelly, Matt G. et al) increase the load and strive to get the time down again!
It's working for me!