Please specify the issue and add screenshots/videos if needed. Mojang cannot fix a bug if they have no idea what it is.
Seems to be fixed in 1.18 experimental snapshot 2.
From the changelog:
Underground biomes interfere less with surface biomes. They can still leak out of cave entrances sometimes though (because it looks kinda cool!)
(Haven't tested it myself though.(
1. feedback for caves and cliffs experimental snapshots must be reported at https://feedback.minecraft.net/hc/en-us/community/posts/4408790359309-Experimental-World-Generation-Snapshot-7-Feedback. THE BUG TRACKER DOES NOT ACCEPT FEEDBACK FOR THESE VERSIONS.
2. If you were downgrading versions, expect buggy stuff to happen.
3. Realms tells you to use the latest stable release of Minecraft available (currently 1.17.1)
4. This bug is useless. There's no screenshots, videos, or logs.
Learn how the bug tracker works, please.