If you boot to both carrier boards, and run this command, does file “edid” exist on both? Are both finding this file at “/sys/kernel/debug/tegradc.1/”? If found, what is the content of file “edid” on both…do they match, or do they differ? Are both found in the same directory?
find /sys -name 'edid'
Normally I would not expect GPIO changes to be a problem, but changes could if the GPIO had previously been used for some other purpose and then suddenly the other purpose had been broken For example, suppose changing GPIO of something which detects video suddenly went missing…that’s just a contrived example, but it illustrates the idea. From both the developer carrier board and the custom carrier board, what is the content (use “ls -l /sys/class/gpio/*”, you’re just listing files, and for the case of symbolic links, where they point) of “/sys/class/gpio/”.
Note that monitor detection of EDID uses the i2c protocol, so if a change to GPIO broke i2c it might break the creation of the “edid” file (which is a result of monitor EDID query over i2c).
EDIT: On both carrier boards, what is the content of: