the brake calipers may have distorted pistons. I had pistons that failed as you are having your issues. the pistons get bell shaped. with new rotors and pads the piston is fully in the caliper. as the pads/rotors wear the pistons begin to bind up as they come out of the cal bore.
more cheap chinese crap. never seen this before. thanks GM , another buck you saved at my expense !
new calipers problem solved. NEW , NOT REBUILT...
Many rebuilt have this distorted piston.