WorldGuard Docs:
/stoplag Remove all entities in all worlds and enter a mode where all physics events and liquid flow events are stopped. In addition, when a chunk loads, all entities in that chunk are removed. The purpose of this command is to solve problems involving thousands of entities or items. However, when this command was added, tameable animals were not a thing and the loss of entities was not an issue, but this is no longer the case and this command should be reserved for extremely desperate occasions. -s can be provided to make the toggle not issue an announcement in chat.