I've enabled today the gamerule to limit the number of entities on the server, known as maxEntityCramming. This is a new setting introduced in 1.11, which I've set to a value of 50. This means that, within a small enclosure, any mobs over that limit will automatically suffocate and die. This is put into place to prevent runaway mob farms from piling up and lagging the server for everyone.

Note that this automatic check doesn't change anything on what we expect from you: all players still need to keep an eye on their mob farms and prevent them from piling up too much. Thank you for keeping everything running smoothly for all players!