B767 Captain reported Relief Officer noticed the left fuel quantity indicator was blank and later on; a fuel configuration EICAS message appeared. After consulting with Maintenance; the flight crew performed an air turnback.

Narrative

Climbing through 8000 ft.; the Relief Officer noticed left fuel quantity indicator blank. I continued climb hoping to recover the fuel indication. I asked the Relief Officer to see if there was a checklist that could help us. He couldn't find anything of help. During intermediate level-offs we would get the fuel config EICAS message. The center tank pumps were turned off by this point. The monitoring First Officer offered to take aircraft to relieve my workload and I accepted. I contacted Dispatch and Maintenance Control through SATCOM. Maintenance Control let us know that there was nothing he could do for us in the air about the fuel indication. He also said the fuel configuration EICAS should not be related to the left fuel indication problem. In consultation with the crew; I decided a return to ZZZ was the best course of action. We did not want an imbalance to occur and have to guess when to start and stop transfer of fuel over the Ocean. We were still in ZZZ1 airspace. The flying First Officer had stopped the climb at FL270 by now. We got a clearance to return to ZZZ. During descent we got fuel config EICAS and had to turn center tank pumps on again because the center fuel indication had changed from 400 lb. to 1200 lb. Turned them off before landing when center tank fuel low pressure lights came on with 400 lb. showing in center tank. We figured out the varying deck angles was sloshing the center tank fuel around and causing the fuel config EICAS and not related to the left fuel indication problem. I took back control of the airplane and had an uneventful landing. In the air we had sent an ELB (Electronic Logbook) writing up the left fuel quantity indicator and fuel configuration EICAS. We explained our thoughts about the fuel configuration EICAS to the Mechanic.