My opinion for 1 and 2 is the same. For 3 the OP stated that he bumped the lapua shoulder back .002 loose in the chamber.

Number 4

Since the die is not working for the long head space Privi brass, whenever the Lapua stretches more the die probably will no longer size it enough either.
I have found that if the brass is in reloadable condition that spring back is minimal. There may be some people that size hardened brass by adjusting the die to account for springback of the shoulder but I have never known anyone or seen anything written that advocates this. Accuracy suffers. Unequal neck tension and inconsistent shoulder length is a biproduct of such practice as well as split necks etc....

There is always a die or chamber that missed inspection and was shipped out that may not be in spec. Due to the success of the lapua sizing I do not see this as the case here. The experiment of annealing one or two pieces of brass will answer all of the questions though.