Any reason why Decoy Grenades sometimes just don't work?

Was just playing LF and was doing the step with the water valve. I always use decoys and aether shroud to get me through this step and I noticed that quite often my decoys just do absolutely nothing after I throw them. This time it was so bad that BOTH of my decoys just did literally nothing and I died because of it so now I am pissed off enough to make this post. Is there actually something to those decoys that I'm just not getting or are those things just bugged?