Back in the day when Service station here in the U.S. installed brake lining almost every garage and gas station had a brake grinding machine to taper the leading and trailing edges of the new brake shoes so they would break in properly and no tmake the centers not touch until the edges where beveled.Thye called that "Arcing" the shoes I'm wondering if the front and trailing edges are growing more then the centers when appleid making them bow up (grow) until they start rubbing, which makes them heat up and grow more
Let us know what you find to fix it, maybe run them looser for a while until they seat properly