I am having issues with X
I read this backwards and deleted my answer. I thought you enabled serial then it wouldn't boot.Having disabled the Serial port on the MB. I can no longer boot 13.1 yet 13.2 boots just fine.
At the loader prompt you can try this too.hint.uart.0.disabled="1"
set hint.uart.0.disabled="1"
set hint.uart.1.disabled="1"
boot