It sounds to me like you've got a bent backing plate. If the drum was warped, the tight spot would rotate with the drum. Pull the drum and the brake shoes back off, down to a bare spindle and backing plate, and do some measuring from the end of the spindle to various points around the edge of the backing plate. If it's bent, straightening it might be a real challenge. I'd expect uneven brake shoe wear if it's allowed to stay out of alignment.
Jerry

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