Q: Stuck brake caliper

Although it is possible for a collapsed (internally and thus "invisible") rubber brake line to cause a retraction failure, by far the most common scenario is the caliper is sticking. If the calipers have more than, say, 70,000 miles on them, essentially they are not re-usable without re-building. There is an internal seal in the caliper bore and the operating conditions are extremely harsh including continuous corrosion and extreme heat.

I have learned the hard way that the only way to have any reasonable assurance that disc brakes will work properly, if they are present as "worn out’, is to automatically discard the calipers and torque plates and buy loaded re-built calipers from a reputable vendor such as AC Delco or better yet, through an OEM dealer rebuild source. You may also have sticky sliding bushings in the torque plate, accounting for the stickiness you are seeing so you can check that out as well. But, again, if you have north of 70,000 miles on the calipers, just trade them in and save yourself a lot of headaches and unusual wear patterns on your brand news pads and rotors.

Have a certified mechanic, such as one from YourMechanic, come to your location to perform a brake inspection to determine the source of any sticking and suggest repairs.