It happens because there are no non-transparent blocks around the end_gateway on the central island.

Workaround: put at least one full block inside 11x11 area (at any Y level) around the end_gateway block

Hardcore mode game created on Minecraft 1.11.2;
Map seed: 3301641908054965261

After teleported to the outer island with End Gateway Portal on central island by using Ender Pearl, I found myself unable to be teleported back to the central island with End Gateway Portal on outer End island.

When trying to use end gateway portel on outer, it teleported me back beside the Portal on outer. (2017-03-15_02.38.11.png) By watching my location (with F3), I found I was excatully teleported back to the central island, but the location where I arrived, is the block right upon the portel of central island. (2017-03-15_02.38.18.png) Which means I was teleported back and fall into the portel immediatelly, and got 1Hp (0.5heart) suffocation damage when teleported in to bedrock.

All of this is confirmed after I recreated the game map with creative mode and tested them. 2017-03-15_02.39.34.png shows the location where I arrived on central island (I removed the bedrock with creative mod)