One side of my back is tighter than the other. Things to take notice of are;
-Side bridging times on each side(are they equal?)
-Do you feel your whole abdomen from left to right to up and down burn evenly or do you feel it mostly on one side/section?
-Can you contract each glute as evenly on both sides. Test it via the single leg bridge, this'll show your weak glute
-One quad or hip flexor is probably tight on one side
-Test to see which piriformis is tighter via stretching it and work on doing some side lying clams and fire hydrants pre-workout
-Test left vs right side strength in bulgrian split squat using bodyweight. My left is weak and unstable/balanced compared to the right
Usually testing these areas will help you pin point where the problem could be.