I agree with Dana, I’m betting you’ve been getting 11x2.5” drums. The deeper drum hits the backing plate before it bottoms out, and pulls the axle.
The axle flange offset is the same for all BBP drums, so, the backing plate offset has to be different for different widths. So the backing plate for an 11x2.5” drum has more offset than for an 11x2”. The 11x2’s are harder to find, and I would bet money most parts shops aren’t giving you a C-body or truck 11” drum, which is where most of the 11x2’s were used originally. If you aren’t careful it’s easy to get an 11x2.5”.
