Before the auto-jump implementation, it was necessary to manually make party members - including the ranger animal companions - jump to some spot with available space.
Now, with the auto-jump, the animal companion choose by itself where to jump. The problem is when another party member is underneath, it receives over 25 HP damage. This can instantly kill one of your party member and is very annoying.
I experienced it many times with the spider, didn't try with other animal companions.