Can confirm for 1.17.1 pre-release 1
Can confirm for 1.17. Seems to disappear after the 32-bit signed integer limit (atleast on the Y axis), where even the NBT data says that the beam has "no target". Near the limit, the beam is completely detached from the crystal (very far away), and moves with the players view.
This is a issue with minecraft using BlockPositions (which are just pointing at a block, not a location) for the setBeamTarget method despite the fact that the EnderDragonRenderer class has a method for the same thing, which supports floats for coordinates, that points the closest end crystal to the closest ender dragon.
This bug limits end crystal usage by a lot, as only allowing whole numbered coordinates makes any sort of custom movement look very choppy.
This happens to me on a multiplayer server randomly. The map started in 1.13.2 and has been updated to 1.14 and then again to 1.14.1 pre-release 2. The cache got erased when upgrading from 1.13 to 1.14.
I tested it on 1.12.2 on singleplayer and it is still happening, attachment is a picture of the setup.
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Basically Items go to the side before going down, this might be because of the item elevator but ive seen it on builds without it.
This has been always like this.
Issue is resolved on 1.17.1 with provided example URL.