Update. If I use quick quote to see the post, I can then copy and paste it into a post, enable both HTML and UBBCode, and the post will appear. However, if I try to edit that post, the edit box is empty. Very weird.

The Stovebolt Geek
https://www.stovebolt.com/ubbthreads/ubbthreads.php

Server Information
UBB.threads Version 8.0.0
Release 20240826
Server OS Linux
Server Load 0.11
Web Server Apache/2.4.37
PHP Version 8.3.11
MYSQL Version 8.0.39
Database Size 1.82 GB