the phone also, im sure, uses algorithms to determine the best combination of signal strength vs battery drain. in the same area, you could get one dot of LTE and full dots of 3G/4G. in order to conserve battery life, the phone may aternate between what it feels is the best option. all of this would most likely be due to a current network issue. however, if both networks are fine and this happens often, it could also be a software/hardware error with the phone. but my money is on its more likely a network issue that will resolve itself.