The bug

The changes to biome distribution were unannounced by any official source. The main bug here is that certain Nether biomes are always incredibly tiny and/or can never be as large as they used to. Here are the seed and coordinates for tiny Nether biomes:

Warped forest "microbiome": Radius: 12 blocks. Seed: -1118759503779387613 Command:

/execute in minecraft:the_nether run tp @p -1073 86 -30

Soul sand valley "microbiome": Radius: 36 blocks. Seed: -8511534518682158031 Command:

/execute in minecraft:the_nether run tp @p -228 73 156

As shown, soul sand valleys and warped forests can generate extremely tiny, and if not, they never generate as big as they used to. Also notice that most of the new Nether biomes have been made really rare. Here is the list of biomes and their percentages, in order from biggest to smallest:

• Nether Wastes: 57.278%. This biome practically composes 60% of the Nether, a significant increase from the old Nether biome distribution.
• Crimson Forest: 25.287%. Though the amount of crimson forest has not changed significantly, crimson forests are still smaller and more distributed.
• Basalt Deltas: 8.897%. Basalt deltas are smaller and more distributed.
• Soul Sand Valley: 6.820%. Soul sand valleys are way smaller and rarer than they used to be, making soul speed less useful.
• Warped Forest: 1.718%. Warped forests are super rare and often too small to keep you safe from the Nether's dangers.

This is unbalanced compared to the old generation, which had fairly even biome distributions.