Map minimap Mechanic locations not always reveal after defeating the Map Boss

After defeating a Map Boss, usually all mechanics on the map show up as well as their "quest" icons.

Very good feature , that indicates you that you can leave the map after doing stuff that you need and not waste time exploring full layout.

But they dont show up always. Some bosses seems to not reveal the mechanics and themselves dont show their icon on the map. Some bosses show their icon on the map , but still dont reveal anything after death.