Every so often there's a bug with one of the gilding triumphs that allow players to obtain the seal without doing the base requirements, in your case you were able to skip the platinum division triumph. When the next season/Episode launches and the gilding triumphs are changed, that fixes the titles triumph count and relocks the title for players that got it via a bugged triumph. It isn't removed if its equipped but it cant be re-equipped until either players get the bug again or the do the base triumphs. Once you get platinum division and claim that triumph, you'll be able to re-equip it.