[Arizona]

I've smoked cobs for years and never had this problem. My old MM cob from 1981 has some hairline cracks that run vertically along the natural lines of the cob's grain or whatever you call it but they haven't gotten any bigger or resulted in the pipe falling apart.

I currently have 3 MM cobs that I've gotten in the past year and smoke them regularly. None of them has cracked at all so far and they get smoked a few times a week in rotation.

As a cob ages and is smoked many times it acquires a natural darkening from the tars, etc.

Heat is mostly likely the cause. Smoking it way too hot.