ender dragon glitched

so i was respawning the ender dragon while it was doing its beam thing i accidentally closed minecraft. then i opened minecraft loaded up the world and the beam thing was stuck and the portal to get out of the end was gone. after this happened i reset the end though dim1 and the crystals respawned but not the dragon so i did it again and when i loaded it up again i saw the dragons health bar at the top and then it disappeared. i'm not sure what to do now. any help would be appreciated. btw i have looked into it and i cant find anything to help.