A few days ago I created a new survival world on the 20w20b snapshot. On May 20 snapshot 20w21a was released and I updated my survival world to the latest snapshot. On the same day I defeated the ender dragon but the End Gateway portals, which normally appears after defeating the dragon, did not appear.
Now, I have tried beating the Ender Dragon in a different world on the same seed in creative mode and the End Gateway did appear. I even did it twice, both times the End Gateway appeared.
On my survival world I have killed the Ender Dragon three times but the End Gateway portal never appeared. Before the third attempt I selected the 'optimize world' option in the select world menu, but still no Gateway portal.
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Thank you for your report!
However, this issue is a Duplicate of MC-184482.
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Duplicate ofย MC-184482