So I've been rolling this around in my melon and while I can't put my finger on exactly what is going on here are my thoughts.
1. Both loads worked before but now, at the same time, stopped chambering.
2. The odds of both sets of dies, both lots of brass, etc changing on you at the same time is pretty small. The odds of your calipers going whack at the same time is also pretty small.
Think it has something to do with your press? Is something going on there that is adjusting/affecting the OAL without you knowing about it. Or is something keeping the arm from its full course of travel?
New gun, same ol' shot.