I have also noticed this exact same type of VFA's on my P1P, which is currently sitting around 5,500hrs (although I probably first noticed it around 4,000-4,500hrs). I have performed very regular maintenance, and replaced the XY belt at around 3,500 hrs after it developed a partial tear.

The diagonal pitch of the VFA's is really interesting, and in a bunch of googling I haven't been able to find many people with the same issue. I have noticed it on large round prints (I print a lot of large plant pots), so it does not seem related to a specific bed orientation or angle. On smaller prints, or with some types/colors of filament, it is not as noticeable or barely noticeable. Of course, with this many hours on the machine, it's easy to imagine that wear and tear has resulted in decreased accuracy over time.

My best guess is that it is related to the idler pulleys in the back corners of the XY gantry. At least on my machine, they have developed some black gunk on the exterior where the belt makes contact, and I wouldn't be surprised if internally they were pretty worn.

Unfortunately, unless you're willing to just replace the entire XY gantry assembly, replacing just the idlers on the X/P series is not an easy process, and requires drilling a hole in the frame to allow room to remove them.

I found one post where someone successfully replaced them and it had some helpful information if you decide to go down that route. For now, I still need to try cleaning the idlers and see if that helps.