Purge never attacks

I’ve been playing single player for about a week and over the weekend I set up a dedicated server. The purge was enabled on both and yet I’ve never had an attack. My purge bar would fill and drain at random but the attack never came. Am I missing something?

I’ve never had a purge spawn either. I’ve filled the bar to completely full almost every day since the update, but not even once has it spawned.