Not sure if this is/was your issue, but had a hanging brake on a front caliper after doing a thorough brake job (removed everything, cleaned everything, painted everything, new bushings, bolts, sliders, brake lube, etc.).
Turns out the caliper slide pin holes are a blind hole and when I applied the brake lube to the pins and holes, the lube got trapped in the blind hole ahead of the pin (which just happened to form and airtight seal in the housing). It was enough to cause the brake to drag after the caliper was no longer floating. Took me a while to figure it out. Removed excess lube from hole, re-install, and everything was OK after.