Decoration generation isn't based on seed, making it extremely difficult to reproduce decoration related issues. It probably causes other issues, such as decorations getting cut off on chunk borders.

To reproduce, use the seed -6908976867497675196 and run the following command:

/execute in minecraft:the_nether run tp @p -511 79 -421 -90 0

An extra huge warped fungus should generate in front of you. Create a new world using the same seed, but run these commands instead:

/execute in minecraft:the_nether run tp @p -543 77 -428 -90 0

/execute in minecraft:the_nether run tp @p -511 79 -421 -90 0

The large fungi distribution has changed!