Somehow its built wrong. I would suggest getting a pin spanner and removing the outer lockring then the bolt and not removing the arms. See if the splines are actually lined up. I've seen these installed where it was a slightly tight fit so it was assumed things had been lined up and instead it was off by a few degrees and the bb cut slightly into the crank splines. Because it wasn't all the way it was possible to pull the crank and reinstall properly. But you want to look. If this has happened and it cut too deep that arm is garbage. If this isn't it, I've never heard of the arms or bb being milled wrong but anything is possible, I have seen other cranks bent out of straight by BMXers but that seems equally unlikely for road cranks