Check the static torque on the Quarq. If that checks out, either the stages is off or you have a very weak left leg.
In order to rule out the left leg issue, you can do a test where you pedal left-leg-only and see if that gets them closer to matching.
Another possibility is if the stages is intermittently dropping out (many people have reported weak battery doors. Be very gentle with yours) AND whatever software you’re using reports the dropouts as 0W, that could bring down the stages average significantly.