This world was created on an older version of the game, and the ender dragon was initially defeated on that version of the game. The ender dragon was then defeated after updating to version 1.20.1 and a 2nd end gateway did not spawn. Only after another defeat, the 3rd total for the world, did a 2nd end gateway spawn.
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The dragon was first killed in version 1.19.4
I wasn't able to replicate this myself
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In which version of the world was the world created and in which version did it enter The End?

I referenced my screenshots, the world may have been created as early as 1.19.3. The ender dragon was killed before updating to 1.20.
I was unable to replicate this bug going from 1.19.3 to 1.20.1.
If you could not reproduce the issue going from 1.19.3-1.20.1, please verify exactly how to reproduce the issue, and add clear steps to consistently and reliable replicate the bug.
For the purpose of trying to replicate this, what was the specific previous version you were in when first killing the dragon?
This could also possibly be related to, or duplicated by MC-171797