Regarding armour suddenly being ignored -
From what I understand (which may be entirely incorrect), each piece covers a certain percent of the locations it covers. When you get hit, the game first determines location, then checks to see if the top layer of armour is hit (using that percent as it’s chance of being hit), then the next, until there are no more layers. It then applies the layer that was hit’s protection, determines damage from that, and decides if the armour was damaged.
Sort version - if your armour only has 95% coverage, 5% of all hits are going to ignore it. Less coverage, more hits ignoring it.
edit - and all this is irrelevant, as the items mentioned cover 100, so should be hit every time (unless damage to them reduces their coverage, which would make sense)