Inside of net/minecraft/world/level/levelgen/structure/placement/StructurePlacement funtion probabilityReducer calls another function setLargeFeatureWithSalt with arguments in incorrect order.
random.setLargeFeatureWithSalt(seed, salt, sourceX, sourceZ); is called, when it actually should be
random.setLargeFeatureWithSalt(seed, sourceX, sourceZ, salt); because function that is called acctepts arguments in next order
setLargeFeatureWithSalt(final long seed, final int x, final int z, final int blend)
Which results in incorrect probability.
Turns out, this makes
defaultmethod is useless for randomisation. I`ve made a datapack that uses 2 structure set, one places red columns withdefaultreduction method, another places blue columns withlegacy_type_2. Both sets have the same salt, which should give same result. Butdefaultremoves lines of structure attempts in Z cardinal direction instead of expected randomisation. It is expected that both columns would spawn at the same position, one over another. Datapack that reproduces it attached below for version 26.2.