First end gateway not working.

On a fully survival world, i beat the enderdragon and the end gateway appeared. I went through and everything was fine. But i went to a end city farther away and i saw a random gateway that spawned on an island and so i went through that to get back to the main island. But when i tried to go through the gateway on the end island, it just teleported me a couple blocks away from the portal to the overworld. I left the end, came back, and tried again. It still didn't work. Then i tried reloading the world and it still didn't work. Then i was like "oh ill wait for 1.16". When 1.16 came out, i went into the world and it still didn't work. I then re spawned the enderdragon and a new gateway appeared. The new gateway worked but the old one still didn't work. If you need the world, i will include it.