Solving Raspberry Pi Compute Module Booting Problems
As of late 2015 a new version of the memory card driver (sdhost) has been adopted in the Raspbian firmware/kernel, this unfortunately doesn't play as well with the eMMC device on the compute module and causes a problem, as noted on the support link below, which results in the boot process to freezing ocassionaly during the boot cycle.
As a work-around to fix this is to specify that the system use the more reliable older mmc driver instead, to do this add the line below in /boot/config.txt.
dtoverlay=mmc
Follow the issue directly on GitHub here :
https://github.com/raspberrypi/linux/issues/1317