There are differences in power consumption when using Nothing earbuds for different purposes. The peak of power consumption is during a voice call.
It is normal that the percentage difference between the left and right earbud is less than 10% when using them simultaneously.
Please makes sure you are using the latest vesion of the Nothing X app from either Google Play Store or IOS App store. To check, go to Settings > Firmware Update in the app.
If this does not work, press the button on the charging case for 10 seconds to do a factory reset.