[Q] Unable to Flash Kernel topic

Hi. I have been having issues flashing kernels on my M8.

Some background:
Security: S-Off
Rom: Digital High GPE
Firmware: 4.16.1540.8
Recovery: TWRP

Problem:
I am currently trying to flash the codecraft kerenl on my device (though I have encountered this problem on other kernels). When I flash the zip (after doing a dalvik and cache wipe) in recovery, the phone automatically boots into bootloader after showing the HTC splash screen. No matter how many times I try to reboot, the same thing happens. I am able to access recovery when this happens so I have been able to restore nandroid backups in order to boot my previous rom/kernel.

Am I doing anything wrong/do you have any suggestions?

Thanks!