first of all, thanks for the very good report, it really helps us when we get all the information we need
As you know, there is no set of bootloader for the board, publicly available. So like you, we are using 'internal' android releases for proprietary blobs. The release you are using is slightly older than the one we use..
anyways, when we moved to a recent release a couple of months ago, we noticed that support for splash screen was enabled in LK (in Android builds), so that you can see the snapdragon logo very early in the boot.
The splash screen support creates issues with the linux kernel, as we don't have proper handoff of resources between LK and kernel yet. I suspect this might the be issue you are seeing, so let's try to disable it, put the board into fastboot mode and run
fastboot oem select-display-panel none
it should be set to 'hdmi' by default, and you should be able to revert to hdmi with
> fastboot oem select-display-panel hdmi
after you set it to none, please power off/reboot and try booting linux again.