Comparing the lap times by the video timestamp, the first full green lap ran ~1m50s and the last ~1m54s. That's a big difference. There are a lot of factors at work here- settling into a rhythm, following the lighter, faster CANAM car, tires going away, running alone on the track, etc. Four seconds is a big difference...
As for the brakes squealing, that may just be a factor of them heating up. That's part of running a race pad- some compounds may tend to squeal a bit. I'd wonder if the feel and power went away or just the noise kicked up.
Maybe John will chime in with some commentary here?
Chris