It was supposed to make the Wizard invulnerable yet certain skills can remove the Ice Crystal completely or the damage over time can kill the Wizard inside the Ice Crystal.
It wouldn’t be a problem if other classes with damage immunity or untargeted or invulnerable could be killed by damage over time but apparently, it is not. Only the Wizard can still die in the invulnerable state.
Cold Calculus is the only invulnerability skill that Wizard has yet it is so pathetic and buggy.