Please note that, In MongoDB, when you drop a collection or index, it may not be deleted immediately. Instead, it enters a "drop-pending" state, especially in replica sets, until it is safe to remove—after replication and commit across nodes. The "ObjectIsBusy" error means MongoDB cannot proceed because the object, such as an index, is still active or not fully deleted.

This status is internal and usually clears automatically once MongoDB finishes its background cleanup.

As you said it is fresh mongo that curious me if there was already older version of mongod ran and abandoned? If it is fresh you can clear the dbpath and try start them

Thanks, Darshan