The "Mystical" versions of the Giant Frost and Giant Thunder runes have their chestpiece and amulet effects swapped with each other.

AKA Mystical Thunder Rune gives water resist and movement bonus, when the normal version gives air resist and dodge percentage.

https://imgur.com/a/N1KDI a visual representation

Could technically be intentional, but no other Giant Rune changes its effects when adding a Mystical Rune Frame, so seems like a bug.