Drum brakes question

A rear wheel on my Tomberlin is dragging badly. Noticed it while testing my new 8kw motor on jack stands.
Might have been that way for a while.
Took the wheel off to look and problem went away.
Tighten the lugs problem comes back.
Put shims behind the drum, no change. Still locks up when lugs are snugged.
Something simple, right?
Looks clean inside. Shoes move around with slight force to center them.

Air in brake line or piston?

Wheel spins freely with lug nuts loose. Drum plus off easily.

Bent backing plate? Causing the drum being forced into the backing plate when you tighten the lug nuts?

I had this same problem on my 08 GEM, I don’t know exactly what fixed it. I had the drums turned and knocked the pads around with two 2x4’s to reseat them (used the 2x4’s like clamps but smacked them at the same time from opposite sides). re-tightened the lugs and all was good.

Sounds same. I squeezed with a bar clamp and it helped.
Drums must be out of round. Drags more at one point in rotation.