I've had a couple of .40 caliber rounds that separated like that over the years. One in a 1911 with unsupported chamber and two in a Glock 22. In all of mine it involved either tired brass (Winchester range pickup with 6+ reloads after I got it) or questionable quality (1 Fiochii, 1 Federal). On one piece of brass, the head separated completely from the case walls, requiring me to dig the remainder of the case from the chamber.
I look at the extractor groove and if it appears shorter/narrower, or if the angle at the front of the groove looks to be less than 45 degrees I throw it in the scrap pile. The base of he case takes a pounding in the .40, and actually sets the case back a little on higher pressure loads. If you question the wisdom of loading it again, don't.
.40 caliber and .38 Super require careful attention when reloading.
Hope the comments help.