I tried those bullets and still have most of 3 boxes. I was looking for passthroughs for blood trails, but they are so hard to load I gave up on them after 3 or 4 shots. You could barely get one down the barrel.
I believe you must have had low velocity. This is why: I shoot 345, 360, and 375 grain lead bullets. They mushroom extensively and almost always make the off-side hide. Your bullets mushroomed none, remained fairly sharp pointed, and still stopped on the offside. To me this says they had much less energy, or such a streamlined bullet would have gone through like a full metal jacket.
Maybe your entire can of powder is bad? You should chrono a few shots from it. I could see the load in the barrel being wet, but then to have the loads in the speed loaders do the same seems odd.
Did you send it to a butcher? Maybe they will find the missing bullet.