This may affect previous versions but I have not tested.
When going through an End portal in the Nether, the obisidian platform is generated in a random spot, but not where the player appears in the End. This is likely related to MC-169008, although that bug seems to be older than this one.
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Actually, the platform does generate, but it no longer generates in the correct position. I assume this has something to do with the obsidian now regenerating every time an entity goes through the portal.
I've update the ticket accordingly
(Which I think means this isn't really a bug, but that MC-169008 is and needs to be fixed)
For me in 21w08a, it is not random, the obsidian platform simply generates one block higher than when entering from the overworld.

Please check if that's still an issue for you in the latest 1.16.5 stable release or the latest 1.17 development snapshot.
Can confirm, interestingly, a few snapshots ago the platform did generate, see MC-177910