Board Thread:General Discussion/@comment-37571800-20181120161358/@comment-29325824-20181120161951

Simple. Captain-Commander is the official rank of the leader and highest-ranked member of the Gotei 13. Kenpachi is an unofficial title given to the greatest swordmaster of the Gotei 13, who due to tradition happens to be the Captain of the 11th division. Personally, it might be possible to be both a Captain-Commander and a Kenpachi at once, but probably highly unlikely.

I personally don't see much if any conflict here.