Server crashes when too many people join at once

So when a lot of people join a server really quickly (e.g. 20-30 people in 1-2 seconds) you can't flick levers, and soon after it crashes. This does not happen when the same number of people join the server but more slowly. I am not completely sure what is causing the crash exactly, but I have attached the crash log.

Note: Please don't think this is not a bug because it does not affect many people. That does not mean it is not a bug. Also, if you are wondering why I would have 30 people joining my server in one second, please read this: http://www.reddit.com/r/ultrahardcore/wiki/playerfaq#wiki_how_to_get_into_a_match