MC-189968
This is the new bug report "Mobs Suffocate in World Border"
Hopefully this works for you, and thanks for looking into my bug reports!
Alright, thanks for the information! I'll get onto creating a new bug report for the suffocation and will keep it more brief. I'll include a new video that will just show the mobs getting suffocated in the border.
I tried using that seed and went to the places in the screenshot and none of them matched and I was in complete different places, are you able to check to see if the seed is the same as you posted in the Description? When I use the seed 67965268637732200777 it changes it to -470642658 so something might have gone wrong.
I saw this issue before with a friend. They had to re-summon the dragon with end crystals to get an End Gateway because the first dragon didn't give them one. Best of luck to you and your world though!
Testing this in 1.16-pre7 it doesn't seem like mobs suffocate in the border anymore.
I made a short demonstration of this: https://youtu.be/bJNhwfV5fSs