Beaglebone: Unable to boot with custom cape
LCD_DATA0 ~ LCD_DATA15 configure boot priority during the boot process and are called boot pins. These pins are internally pulled up/down by a set of resistors. According to BBB reference manual:


  If you plan to use any of these signals, then on power up, these pins should not be driven. If you do, it can affect the boot mode of the processor and could keep the processor from booting or working correctly.


but you have utilized boot pins in your application. ensure that cape signals do not interfere boot process. check BBB schematic and reference manual for more information.