After killing a dragon in my world the gateways won't generate.

I did try to copy my world and put it into creative mode and then slay the dragon 3 more times but the gateways won't show up. Also after getting to the end cities islands ( by building a bridge) I did discover a gateway that took me back to the main End island but the gateway that should take me to the other islands did not appear. I managed to slay dragon on 4 more random worlds i created and the gateway appeared only on one of them.

I think it might be because of the snapshot because friend of mine told me that, Mojang was doing something with gateways lately.

I can provide seed to my world if it is needed

Dashi