This problem exists either as an error in the wording or an error in the execution of the Apocalypse traits.
Rather than saying that creatures “gain” stats, Apocalypse traits state that creatures simply “have” higher attributes - be it stats, damage, crit damage, depending on the creature - thus making that the new norm/baseline. This suggests that the game would handle these altered stats differently when things like death occur, and creatures would not lose these stats, as there is nothing to revert from, given that these altered stats are the new norm. They ‘have’ them. They have ‘gained’ nothing.
However, just like gaining stats, these stats are lost on death and revival. This is not reflected in the wording of the trait, as stated.
Is this an error in the game’s execution of these traits, or just wording? Consistent wording is important, especially in a game as broad in scope as this one, and one or the other needs changing.