Since version 1.0 was released earlier today, the server runs fine until one specific player joins. He's in my Discord server so he knows it's happening. It's not a malicious act that is causing this. I use Battlemetrics, which announces when a player joins. Whenever someone joins, I open the Steam overlay to see who joined. A few seconds after he joins, every time since 1.0 was released, the server crashes.. He attempted to join another server and it timed out on him. That server probably also crashed.
In the attached log, you'll see him joining at this point:
18:36:51 [Login]: Adding player Survivor (189404022) to login queue at position 1