Your photo is not coming through on my end. I'd start by calibrating the pedals with the Garmin Connect App or a compatible device to see if any errors are displayed -Garmin Pedal Power Meter Calibration Error Codes What are the pedals connected to and where do you see the -30% value? Check out What Are Cycling Dynamics? for more info about balance data.
It is a known error in Garmin. You can replace the battery door kit, but without solving. Try unscrewing the battery door and screw it until the pedal LEDs light up. The battery door will remain loose, see if the balance indication returns to correct. In various tests I have seen that by leaving the battery cover loose the power meter returns to indicate the right-left balance correctly.
In the past I contacted Garmin support, the pedals were out of warranty. The repair was very expensive. I bought the Favero, also because the support is TOP.
With the Garmin I started to do some tests to understand what they had, I saw that by leaving the battery cover loose, they work 100%.
I cannot recommend intentionally riding with battery doors "loose," and there is not nearly enough info here to assert this is a "known error."
For Rally power meters, use a 4mm Allen key to tighten the door to 5Nm. Towards the end, the resistance increases gradually as the O-ring becomes compressed, but then it should quickly feel ‘tight.' For reference:Best Practices When Changing Batteries on a Vector 3 or Rally System
