The bug

There is an ice spike going from ground level Y=63 up to Y=235. It goes through a floating island, so I guess it has something to do with the bug.

To reproduce

Seed: 97724
Coordinates: -621 70 -327

The ice spike can be found northwest of spawn, and you may be able to see it from spawn if your render distance is high enough.

Frequency

There are no other examples of this bug in this specific biome of that seed, although some more ice spikes generated below ground and look like they are supporting a kinda-floaty island (see the second screenshot).