I'm getting his shield down, then I do the rock method and just wait behind it. It's happened several times now...3/4, 1/2 and 1/4 health left. I'm behind the rock, and all of a sudden I stop hearing any shots, his health stops going down, and I look up and he's gone. The only way to get out is killing myself. I try to stand up every now and then to make sure he's there, but he still disappears.
Does anyone know why this happens and how to fix it?