There seem to be certain creatures that aren’t affected by bleeding even when the right type of damage (cutting, piecing and ballistic) is inflicted. These enemies include the skeletal zombies and the insects. For the insects I can’t understand why this is as they do seem to leave behind insect blood if killed but they don’t get the bleed effect if shoot, stabbed or otherwise. I also don’t understand this for the skeletal enemies since they are just zombies with ossified skin. You would expect that if you riddle one with bullets or manage to make deep cuts in them with a sword that they would be bleeding but somehow they don’t.
Edit:seems sludge crawlers also don’t bleed