gateways not spawning after killing the ender dragon

In my hardcore world, I wanted to kill 20 ender dragons for that i could get the 20 gateways all around the end city. Strangely, there are only 14 gateways, i fought other ender dragons to see if i could make the 6 missing gateways spawn but they didn't spawned. what can i do, i really want to get all the gateways. i have a video showing the gateway situation but i dont think i can send it here. also im playing on version 1.19.4