B757 First Officer reported a fuel quantity and totalizer malfunction in cruise. The flight crew elected to divert rather than continue ETOPS with an unreliable fuel quantity indicator.

Narrative

Fuel quantity maintenance. Upon coming back from my scheduled rest break into the flight deck; I noticed the Captain was talking to Maintenance Control over the SATCOM. The flying First Officer was checking weather in ZZZZ for a possible diversion. We had determined that the fuel quantity indicator was not working properly. The right tank indicator and totalizer were turning on and off and the left side quantity indicator was showing 1200 lb. or so low; and then returning to its normal value. The center tank pumps were on and working; but the wings were showing an imbalance; without a FUEL CONFIG annunciation. There was also a status message annunciation about the fuel quantity indicator indicating a malfunction. This fuel quantity indicator was also written up before for erratically turning off and on the right side. We decided that the best course of action was to divert to ZZZZ as an unknown fuel quantity reduces safety margins considerably. We turned to ZZZZ and conducted the diversion checklist to make sure we had everything completed prior to and after our arrival. The diversion was uneventful and we got to the hardstand without further issue. Passengers were deplaned; Maintenance was called; and preparations were made for accommodations.