What did I do

I just placed a large amount of gravel and then removed a bit of it.
Result

• Windows told me that the client isn't responding anymore.
• Server told me Client lost connection.
• Client told me I'm still on the server (had to kill it with the task manager). - Server crashed a bit later.

What did I do

• Then I restarted the Server and the Client.
• I Joined the server and yeah, same stuff happened again. Well, at least the Client was able to be closed with the quit button instead of with the task manager. But the server crashed again.
  I uploaded the picture which Minecraft showed me before the server crashed after I restarted the Server.

How to fix the world
From my experience with this problem in Minecraft 1.10.2, download MCEdit and remove the complete chunks or delete the complete world or restart the server several times and hope that it some day works again.

How to reproduce:
After reading the log files, it should be clear. Place a lot of gravel or sand and remove some of it, so that everything falls down.

I hope this crash get's fixed before 1.11.