I think I know where the discrepancy comes from, but I'm not 100% certain yet...
The Soviet figure of 46,000 lost aircraft in combat induces aircraft destroyed by enemy aircraft, ground fire and missing in action/failed to return.
The Luftwaffe figure of 45,000 Soviet aircraft destroyed in air combat includes Soviet aircraft shot down by Luftwaffe aircraft, and ground fire.
The Luftwaffe figure of 77,000 Soviet aircraft destroyed includes Soviet aircraft shot down by Luftwaffe aircraft, ground fire, and destroyed on the ground by bombing and strafing.
Apparently the Soviets did not consider uncrewed aircraft destroyed on the ground as "combat losses".
I'm not 100% sure yet, but I'm still investigating.