I have already generated one gateway in a survival world but after fighting the dragon no additional gateway was generated, I replicated this by reloading the save file I had prior to the fight and the same happened again.

I then travelled to the outer end and found an additional end gateway near the first one I already had, teleporting through it brought me back to the obsidian spawn platform in the end.

I am unable to attach my DIM-1 file as a zip due to the size that I believe would be needed to replicate the issue.