This bug is really hard to reproduce by the fact it is entirely random. Sometimes, weird platforms can appear around the same place. It occured to me 2 times on the same seed. One time with stone and the other time with half coral fans, half air.
Seed: 962413370393849
Command to teleport: /execute in overworld run tp @s -231.64 67.37 -185.16 -584.10 39.00
A normal generation
Stone platform 1 block above the water (y=63)
Semi-coral fan platform 1 block under the water (y=61)
Note that these platform got the size of the chunk that they are in.
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