could be a partially collapsed flex hose. when brakes are applied, the fluid can pass through the restriction(fluid is pressurized with your foot). fluid can't return through the restricted line upon release(low, passive pressure). to check, raise the RF wheel off the ground. have a partner apply the brakes. YOU apply presure to your raised tire as if you are going to spin it. have your partner release the brake. wheel should spin freely IMMEDIATLY upon release. try it a few times. if there is ANY delay and the wheel drags then releases the hose is collapsing and needs replacement. other thoughts, could also be stuck slider on that side. is the outboard pad thinner than the inboard? caliper COULD be sliding under apply(normal) and not sliding back on release holding the outboard pad on causing drag and heat. TWO possabilities. hope it helps.