Thank you everyone who has been waiting patiently for this - this hotfix brings the game to version 0.14, and it fixes the spawning issue that was appearing intermittently on launch. Formal patch notes are as follows:

• Fixed an issue where it sometimes became impossible to place new creatures despite having met the preconditions & having enough life points
  

We've tested this internally but please let us know if there are still issues. You can do so on our Steam forum, official forum or Discord.