My seed is : 4112039469829789750
when I reached the end, I found there was an end "city", and an end ship, right there (at the center).
when I killed the end dragon, the end gateway (that was suppose to take me to the outer end islands) would teleport me back to the center of the end (my guess, because it "thought" it's an end city gate; those take you to the center).
I had to build a 1000 block bridge to reach the outer end islands.
after some exploring there, I found another end gate way, that took me back to the center; and when I got there, the end dragon was a live again (the life generators for the dragon, were not active).
in short, strange. maybe a very rare bug, but might be a good idea to look into it.