Under "Manage>Privileges", you can select wether you want to edit the perms of a category, or the perms of "global".
You have to go to every category and edit the "guests" so all the boxes are unchecked.
So, I tried opening a bug on github, but the devs couldn't replicate the issue on their end. Would anyone be able to point me in the right direction? eg the code that is responsible to making new replies "live stream"? I found a few candidates to investigate