Hi. I have had this issue for a couple of years.
It's ok for a while (but only about 200 miles), if I adjust the shoes up on that side, which is usually a couple of clicks (offside rarely needs tweaking up) .
I thought it may be due to those recesses that the handbrake pivot can make in the brake plate, causing a sudden jump in cylinder movement, though have welded those up and smoothed the surface.
Rear brakes both working ok for MOT, though nearside, was grabbing more.
Always a lot more shoe dust in the nearside drum/area, as though working harder?
Have changed cylinders, in case sticking, still the same and bled,bled and bled.
Also the cylinders seem to move smoothly across the brake plate, with the shoes/springs removed.
So wondering.
Adjuster slipping somehow?.
Drum wear out of spec (though have swapped them over and still same issue on nearside) ?.
Worth trying new cylinder clips (black best. Iv'e heard), in case there's bit more tension, than a rattling good fit.
Any clues great please and have a H.N.Y
Cheers, Dave