To be clear, you took no damage from the first casting, but full damage from subsequent ones?
Had a theory that the “prevent damage” part worked but the immunity was late in taking effect last time this was reported, but OP wasn’t too clear about exactly what transpired:
Presumably doesn’t affect the normal Ice Block because of a bug(?) which persists the “prevent lethal damage” effect until the end of the turn:
https://github.com/HearthSim/hs-bugs/issues/1175