I’m not saying this describes you but most people have back pain because they sit way too much (like all day) and they have postural imbalances from all that sitting (tight hip flexors) and flabby abs.
If you couple cycling with the average body you end up with over developed quads and a greater muscle imbalance. What can be done?
Core work and general body conditioning
Weight lifting and strengthening the posterior chain
Stretching hip flexors if needed - yoga?
If any of that sounds familiar google “lower cross syndrome” for further reading.
I doubt the slight imbalance measured in the pedals means that much.