What are unreferenced fossils (INFO FOSSIL_UNREFERENCED Found)? What causes them? How to remove them?
They are fossils that are not referenced by any of the existing snapshots at the time fossil collection was run.
Normal prune operation: when snapshot is removed, any unique chunks it referenced are now unused and are turned into fossils. If later passes don’t find snapshots referencing them → that’s your unreferenced fossil
Don’t remove them manually. It’s a safety feature. They will be cleaned up as needed by subsequent prunes.