Same here on two different GNex's. Called Tech Support since the corp store wouldn't give me another exchange. (They couldn't replicate it in the store). Tech Support is sending me a new SIM card too.
The store said if they gave me another device, and they found no problem with the one I sent back, They would charge me full retail for the phone. Tech Support said that was BS, but he couldn't send me a replacement since I purchased in store, and they have no CLN replacements in stock.
Hopefully the SIM card will help, but I'm not holding my breath. Though, I may go back in the store and do just that until they exchange it. LOL.