Ch6, Key for prisoner is not where bloodb's guide shows (this time through playing)

[Bloodbuster]

The keys will not appear until the cut-scene has played out.

You'll see this in Mole Temple. If the key does not drop by the beast you have to kill before unlocking the laser-door, they will be in the rubble. But, they will not appear until after you have approached the lasers and been told that you need to find a key.

[jiminator]

mole temple, the issue is that the key drops when you kill the beast, but if you do not pick it up quickly enough it will vanish to the random place mentioned.