It is quite common for caliper slide mounts to lockup... then break loose as things cool.
When they locked up on my prior car, I would take'em apart, clean them up, lube them up, install new end boots, swap out the rotors and... a year later, same thing. (no racing or riding brakes)
Mechanics and parts stores would want to replace the calipers... umm, non-sense.
Permanent solution was to use a high-speed plugin drill with a 2" diameter steel wire pipe cleaner brush to hone out the caliper slide mounts; and clean up the sleeve pins. Then lube them up with *quality* new rubber parts and rotors.