This happen sometime since the 1.8 on some server, more often if they are highly loaded.

All the players get a timeout, it's unreachable, but.. all the command from console work and the server continue to display /tps right but /stop never end.

The server cannot be joined anymore, the CPU usage increased to 100-400% (depending of netty thread).

As you can see on the screen there is 2 netty thread in infinite loop, still on the same task.
I join to you the screen and the snapshot from yourkit.

Thanks.