You need to check the cylinder

To see if the less worn side cylinder is working properly, any scoring or pitting, any leak, etc.
Also, check the less worn side if the bracket is tightened, the slide pin is still sliding, the pin boots are still ok or damaged. Better change a set of slide pins and regrease the pin before insert. If none of these, then possible the brake fluid line for that side is blocked. In short, any thing on that side could cause reduced force applied to the pad while braking would cause that problem.