Again a new screenshot and new information about Elex have been released by Piranha Bytes on Facebook. This time the post is about the placement of the monsters.

None of the creatures you'll face in ELEX is spawned randomly. Each monster is carefully placed by hand.
- Piranha Bytes

In the comments beneath the post Piranha Bytes also explaines that some monsters will respawn, supposedly at certain points in the story, and that these respawns are placed by hand as well.