It is not a bug, this means those characters do not have upgradeable card yet (probably never will to be honest).
If anything, the fact that Sage Mode Naruto and SoSP Naruto have only 50% link with ninjas they should have 120% (like, you know, his own parents) is more of a bug.
This post was last edited by Aerth on 2023-02-10 04:00:35.