MC-88371 appears to be a similar issue, but how the dragon descends does not seem to be the same.

The bug

When all the bedrock at 0,y,0 is removed in the end, the ender dragon will slowly move vertically with a fixed x/z coordinate when it attempts a perch.

Steps to reproduce

1. Remove all the bedrock from the end exit portal at the 0,y,0 column.
2. Wait for the dragon (natural or summoned) to attempt a perch.

Observed results

When the dragon begins an attempt to perch, it will flap its wings rapidly at the same x/z coordinates while lowering or raising itself at a constant velocity. Naturally-spawned/crystal-spawned dragons tend to move downwards, and can ignore the y~40 solid ground, while dragons spawned with /summon tend to move upwards (though one was observed to go downwards as well).

Expected results

The dragon proceeds to perch above the exit portal as if the bedrock were still there, OR the dragon does not attempt to perch at all.