I started having similar problems and it required either a restart of the phone, switch 4G to 3G back to 4G again and got frustrated. I suspected it could have been related to a setting I tweaked in Llama or Smart Actions. I trouble shooted it to Smart Actions so I deleted all my events and created one for Charging that specified Cellular Data enabled. This fixed it. I've since gone back into my Smart Actions and ensured that this setting was being forced.