All the OP stated was that slightly adjusting the die down fixed the problem.
I don't find him stating anything about "cam over", "press flex" or other possible problems.
Excellent point! I was going off something the OP said earlier about following the manufacturer's instructions on adjusting the die. If he did that correctly, the mouth of the die was already in contact with the shell holder, or nearly so. When he said he turned the die in just a little more that allowed cases to chamber, I took that to mean he was camming over, which is sometimes needed.
Nat seems to prefer shortening the die to accomplish the same goal, which isn't a bad idea...but camming over slightly, isn't a bad thing, either. I don't have the means to shorten a die, so I adjust it properly and if that means the press has to cam over a little, I'm OK with that. I've never broken a die because I am careful in my adjustments. I suppose if I had a die that was grossly oversized I would resolve that by getting a custom die meant for my chamber.