End infinitely spawning ender dragons, causes server to crash

The end loads and a single ended dragon health bar appears. As you move towards the center you can see ender dragons flying in same path. The screen fills with 3 Ender Dragon health bars. There are so many over lapping ender dragons that a definite number is impossible to tell. Appear to be forever spawning new ones since the closer you go the server crashes and reverts to a previous save, long before you were near the end portal.