Exact same issue here, and I am also using Moto G too.
Has anyone else experienced this on different phones? Does anyone have any ideas?
I've put the issue into Niantic's online bug submission but I reckon that will lead to a long wait for answers.
ANSWER - confirmed on my Moto G
Settings > Data Usage
In the 'App Usage' section, click on Pokemon Go and ensure that 'Restrict app background data' is set to OFF (slider should be grey)
Do the same for 'Google Services' and 'Google Play Store'
All three of these apps should be unrestricted.
Now PoGo should work on Mobile Data...turn off Wi-Fi to test.