Edit: double checked the java post and saw that you don't use the bug tracker for the experimental snapshots. So sorry about this, I can't figure out how to delete it.

I found a mycelium island with at least 4 ocean monuments around it. I don't know if this is really a bug or if I'm just incredibly lucky but I don't think they should be spawning this closely together. I am using a couple vanilla tweaks data packs in this world, but I regenerated it using the seed without the data packs and had the same world generation. I thought I would report it on the off chance that there is a bug causing monuments to spawn a lot around mycelium.

Including world gen settings and screenshot with coordinates for a 3-monument cluster.

Seed: 633625694112671524

Shortly after regenerating the creative world, the JVM ran out of memory.