It's fair to consider this a repost, but no one replied with genuine advice, so here we go.

Bullet-based NPCs such as zombies and the Spiderdemon freeze my game once they shoot. I've put on timers that have gone past 20 minutes and the game still hasn't unfrozen.

Is this an addon problem, computer problem, or a wad problem? If you know the cause of this please respond with step-by-step instructions to fix the issue as I can't talk in GMod discussions.