You didn't say how big is the difference between the two speakers.
Over the years, I have had this type of issue twice, but the difference was subtle and it moved the soundstage towards the left (my left speaker was producing less sound):
a. Once it was fixed by pulling the speaker few cms out, and changing the toeing to match the other speaker.
b. Most recently, it was one of the speaker wire connectors connecting to amp. Once I replace the speaker cable, problem was fixed.
All the best!
Over the years, I have had this type of issue twice, but the difference was subtle and it moved the soundstage towards the left (my left speaker was producing less sound):
a. Once it was fixed by pulling the speaker few cms out, and changing the toeing to match the other speaker.
b. Most recently, it was one of the speaker wire connectors connecting to amp. Once I replace the speaker cable, problem was fixed.
All the best!