The fix involved deleting over 140,000 old unread shoutbox message notifications, all of which were taking up space in memory. We've gone from 13.35 GB usage to 6.32 GB with just this one change.

I apologize again for the slowness and crashiness of the forum over the last few weeks, and hopefully this helps make the site faster and more responsive. I'm especially interested to hear from users that were experiencing issues before, to see if this has helped.