Well, my opening post in New forum game, by yours truly thread suffered something like that, so I tried editing it, but it just made a copy at the end of the thread, without fixing the invisibility. I can't delete that extra one either. I get
Fatal error: Call to undefined method Topic::get_permalink() in /var/www/html/attnam/web/classes/post.php on line 72
If crashes are becoming frequent then the most probable cause is that some file or other became corrupted. It happens sometimes. If it keeps crashing, I suggest you simply download it again. Easiest way to fix it.