I have this problem on three balls. One of them is a trick layout ball (Girard layout on a Columbia Reaction Roll) where I didn't get the pin far enough below the thumb. But the other is an old Roto Grip Gold Grenade from the 80s, a urethane pearl, and I also regularly get the thumb on my XXXL Starburst.
The Starburst I can understand given that I'm usually throwing it straight at spares. But the Grenade is a mystery. I get the thumb but not the fingers (although I get pretty close to the fingers, too). My regular PAP is 4 over 3/8 up, and on all my resin stuff other than the Reaction Roll, I don't have this problem.
Jess