Thread prefix still isn't working. I put in the prefix id, fill out the rest and hit create thread and it refreshes with "Please select a prefix." in yellow. I added the the code to functions.php. Happens before I publish and after.
Just returning to this topic. I calculated the current source code size in bytes for a thread with 100 posts, which is approximately 1.7 MB. If I remove whitespace, the size reduces to around 900 KB. Makes quite a big difference.