The spike at the beginning looks familiar. As others have said, a rescan or reload will often eliminate it.
It seems my Liteys have a hard time getting the speed right at the beginning of a scan.
Another thing I sometimes see at the beginning is abnormally high (40 - 100) PIEs at the beginning that taper down quickly to 10 or less. A reload or rescan can sometimes eliminate this.
The next time I see the spike, I'll try to remember to do a test. It might be interesting to see what happens if I start the scan beyond the place where the spike is seen. If it's an initial speed problem, I might see a new spike appear.