I took my ball back to Imperial Lanes today, to talk to the manager. Between him, the machine maintenance guy, and the pro-shop guy, it was decided that what had probably happened was the ball had a defect or crack or abuse, and the return machine nicked it just the wrong way, and hit the crack, and bang, out came a chunk.
They're still going to try to fix it.
The manager was a nice guy, and took me on a tour of pin setting machines. They are amazing 1950s-tech rubegoldbergesqe contracptions of wheels, belts, baskets, ramps, shakers, and actuators.