Every once in a while, you run into a brake hose that gives you trouble. Sometimes they're easy to spot. Sometimes you can see where the outer layer of a brake hose comes apart.
When you see this, replace the brake hose. Sometimes a brake hose fails and causes a caliper to hang up. You can find these by hitting the brake pedal several times and then opening the bleeder valve. If brake fluid comes out under pressure, it's possible the brake hose has failed internally. What can happen inside the hose is that part of the inner hose collapses and it acts like a check valve. It will allow fluid to flow in one direction but not the other. When this happens, you can have an issue that seems like a faulty caliper, but it's really a bad brake hose. So if you replace a caliper and you're still having issues with that wheel hanging up, check the brake hose. By the way, one of the best upgrades you can do to your brake system is install steel-braided brake lines. You'll be amazed at how good your brake pedal feels after you do this.