5090304 - 5090176 == 128
Too unreasonable for that to be a "random" difference.
I think you will find that the "short one" is missing one compressed block of its initramfs.
Even kernels that "don't have an initramfs", have an initramfs that holds the initial /dev/null and /dev/console as a gzip'd, cpio.
If you drop that off of the kernel, it isn't going to boot, it will panic - -
And as you wrote above, you don't have a serial port cable to read the panic message on.
"Hack is just a four letter word." - - With apologies to B. Dylan