@Szalord and I discussed this at some length in the Discord bugs channel. It appears that if the Backlash shield is on you, no matter how strong it is it will prevent Rock Hard from shielding you even if Rock Hard woudl be the larger shield. To make matters worse, the game will give you the yellow health bar like you have a shield and the combat log will state (absorbed) for Rock Hard, but it is NOT absorbed. It is in fact going straight to your health.
Edit: Ok. I’m informed that I slightly misrepresented the bug. @Szalord can correct me. The end result is still the same though. Dead through Rock Hard (Thick Skin) when you shouldn’t be.