This has happened to me many times. Built several big muffs and one stands out as magical. Same parts, same everything. One sounds sweet, the others harsh. I've gone over it many times and can't find a difference.
You throw in 1-5%, 20% tolerances over 30+ parts and viola, you get the same variation you find in biological species. There are always those outliers that sound amazing (or awful, on the other end of the spectrum).
And the lucky shirt makes a difference.