There seems to be an issue with the moto g, CM 12.1 (nightlies) and the GPS. My GPS receiver stopped to work as well and I could recover it with the following steps in fastboot mode as described on xda-developers.

fastboot erase modemst1
fastboot erase modemst2
fastboot reboot

That even works with the 4.2.2 fastboot packaged in anroid-tools-fastboot.