In the mission where you destroy the Kyra Tea Factory, the sniper on the roof is completely immortal. They will not react to bullets, even after restart. Although this one happens consistently, some other enemies will also experience this bug. They'll be vulnerable to knife attacks (I haven't tried explosives yet), but they won't even stagger when an entire clip is shot into them from point blank range.
Is anyone else experiencing this glitch? How can I fix it?

