How do hydraulic flat tappet lifters fail?

Righty Tighty said
Here are the lifters that are currently out. You’ll see the three on the far left have some marking. It looks worse in the picture, I can BARELY feel the marks with my fingernail. I can’t remember which one, but one of those is #7. The #7 pushrod looked just fine. View attachment 1715614809 View attachment 1715614810

They look like they were rotating
The janky ones had a lot of pressure on them causing the premature wear.
IMHO if it were lack of lubrication you would have seen more damage to the other lifters.