Minecraft loses 18,446,462,598,732,840,960 seeds, resulting a total of 281,474,976,710,656 seeds, for 1.18. Here are the seeds and screenshots of these happenings.
Seed 1 - original
Seed 281474976710657 - almost identical, though different tree locations and biome boundaries.
Seed -7379792620528906220 - different biomes and expected shadow seed
Expected result: It should have 2^64 seeds, edit: including shadow seeds.
Observed result: It has 2^48 seeds.
Linked issues
relates to 1
Attachments
Comments 4


Importantly, given the aim of generational parity between Java Edition and Bedrock Edition, this also applies there as well.
It might be advisable to have MCPE-18739 be reopened as a result.
Thank you.
Can confirm. Looks like the first 16 bits of the seed are completely ignored by pretty much all of the world generation, including biomes, terrain shape, caves and structure placement.
Out of curiosity, how did you discover this?