Okay, the game seems to be sending an "OPTIONS" request, which isn't what should be happening. It should be "POST". At least now, we can confirm that it isn't LM Studio acting up. Formamorph itself isn't sending the request right, which is leading to these problems.
Something you could try is to reinstall the game. That might help clear it up. Before you do that though, please "download" any custom worlds that you have and want to keep. I'm fairly certain they will be deleted from the main menu when you uninstall the game.
Viewing post in How to run a local AI for Formamorph
As I was uninstalling and reinstalling the game I've noticed that I've had the wrong, outdated version this entire time. The reinstall, this time of the most recent version, also fixed the issue. Now the local communication works, and the AI is working as it should.
Thank you very much for your effort, but it was indeed me who made an error somewhere along the way :D