I've had the same thing happen to me with black walnut overlays once. I was shooting in a 58# bow and all off a sudden it snapped!
Or so I thought. It happened so fast and violently I thought my bow broke....In fact it flew out of my hand. When it landed on the ground I looked at it really quick and realized the bow was fine.
Then I thought maybe the string broke..... nope. I finally saw one of the overlays had popped off.
The very first thing that came to mind was that the glue must have failed.....NOPE. The glue (I had used TBIII) had held just fine. The overlay peeled off along the grain line of the overlay.... I slapped some horn on there and haven't had any issues.
I think it just had the exact right angle of force pushing on a weak spot on that piece of wood WITH the grain and POP!
Not to go on and on and on but when martial artists break boards they are careful to align the board in such a way that the are breaking the board "with" the grain not against the grain. Why? because they want to look cool
and break a board instead of their hands.
I have not used PH but I believe what you have described could happen to many kinds of wood given the right circumstance. I don't think it is the kind of wood you are using. But that is just me brainstorming based on my one experience above. I think when you talk about "PH splitting easily" you are on the right track. We don't split wood against the grain. right? why? the same reason martial artists don't break boards against the grain. Chuck Norris could do it but he doesn't split boards. He splits entire forests. So we need to throw him out...
I think grain orientation is the issue. Maybe that piece was particularly dry?