player did not receive "The End?" advancement on dimension switch

[tazohbutreal]

To keep a long story short, I am attempting to find a glitch to consistently skip the end and we need to go deeper advancements for youtube video

This all started because on a fabric server that was lightly modded (all mods were ruled out from being the cause) a player went through an end portal and did not receive "The End?" advancement.

I am here just to ask if anyone has the slightest clue of how this was at all possible to begin with, was this even because of fabric? is this something that could happen on vanilla minecraft?

after spending over a month trying to figure it out for myself, I have found that I just don't have the knowledge to make any progress on this

clip.mp4

(clip of the person not getting the advancement)