Sometimes, the slight difference can be linked to placement differences where one of the speakers is slightly closer than the other. A different degree of toe-in can also have this effect, so make sure they are the same distance away from the listening position, and that they have the same amount of toe-in.
Other times, one speaker is placed next to a side wall, while the other only has empty space next to it. The one placed next to a wall will most likely sound louder as the reflections of the wall will amplify the sound. To combat this, using absorbers on the first reflection point will work wonders. Using room correction software will also help a great deal.
If you still can't figure it out, you are of course more than welcome to reach out to our support team who will help you resolve the issue