So, a friend of mine recently bought a second hand M8, and I tried to convert it to European stock.
(bootloader) version-main: 6.12.401.4
Main version shown indicates that the 6.12.401.4 RUU or firmware flashed, or at least partially flashed, and broke the radio.
You have the Verizon version M8, which is not compatible with other M8 versions' RUU or firmware. You should not try to change to another CID/MID and flash other version RUU/firmware, otherwise radio brick is a known result. Try to revert to stock Verizon RUU as instructed in response to your post in another thread.