To guess, I would say cam lobe was worn unevenly before...or the HPFP was not torqued evenly at 10Nm for all three bolts. But who knows, it is also possible the cam follower was not manufactured well and may have been higher in that area.
Guesses are all one can do. I assume its hpfp has been upgraded given the amount of wear for 8k miles, right? Perhaps the spring or piston cap weren't seated squarely. The piston cap, if oem type, may not have had the oem type center button properly re-seated (see @ 6:20 [ Invalid YouTube link ]&feature=emb_logo).
These are my best guesses.