While on my server, another player ran a fill command for an area of 8,000 blocks with "deadbush 0 replace air 0". (The command was run twice with the same relative co-ordinates, because the first attempt gave him an error in his client and the server). This caused the server to immediately crash. When the chunks in that area are loaded, the server produces a similar crash to the first. I was forced to remove those chunks from the save (which stopped the crashing)

The first crash file below is the initial crash, the second is one of the many crashes that followed.