I'm a bit confused about this issue and it's unknown to me if this is specific to my system or saved game.

I'll start with the context, the saved game I've been running is from snapshot 20w21a and used all the way up to 1.16 rc1. 

Killing the end dragen did not spawn an end city gateway as it should. Nor did it help respawning the dragon and kill it again for a second gateway. 

However, I've tried the same seed on a new world created in 1.16 rc1 and it functions normally there