After using the End Gateway in the main End Island, I loaded onto the corner of a small End Island, I was standing on a solid block. However, I was immediately pushed off the corner of the small End Island, falling into the Void.

I tested this again, went back to The End, but this time I crouched as I used the End Gateway to prevent myself from falling off the small End Island. Results were the same.

Both times this occurred, no nearby entity was the cause of my character getting pushed off the small End Island.

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I tested this again in a different world.

I built some stairs to the End Gateway. After using the End Gateway, I teleported to the outer islands with no problems. However, after teleporting back to the main End Island, I appeared next to the End Gateway with no solid block to stand on, even though I built stairs to it.

On the 2nd test, there were no problems at all.

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To reproduce this bug, use the End Gateway in The End. The bug seems to only happen the first time the End Gateway is used. To restart this process, simply re-enter The End.