I had one like that, there was muck stuck in the seal slot so when the pedal was pressed it nipped the piston. Had to pop the piston and seal out and clean the groove.*sigh*
"new" left rear caliper is bad. sticks when applied. can get it to retract by compressing the piston. lines are clear (replaced in 2021) and flushed with all new fluid, so it's not any of that. damnit!