"If you don't have reception (no signal), here's a quick explanation: THANKS TO S0ul_
It means you flashed a new modem over the MG4 one. It's not a bug, that's because Samsung has changed the format of the EFS partition with the MG4 baseband and now the older modems (MC2, etc) can't read the IMEI from the EFS, hence the failure to register your phone in your carrier's network.
To fix this issue you need only to install MG4 modem from aroma installer