First of all, please explain what exactly you mean by logging/submitting scores to this site. Do you mean writing it here for record purposes? If that's what you mean, you can simply post it into the appropriate page (here, it would be the "Master Challenge" page), and you should include a video as proof that your record is indeed legit. If I'm wrong in getting what you mean, please say so.
Second of all, to my knowledge, the developers of Piano Tiles 2, i.e. Cheetah Mobile, has kind of stopped paying attention to Piano Tiles 2. The game is not as played anymore, and development has slowed. In the same vein, the leaderboards used to reflect real-life, as there were many active players. I think it only contains placeholders now, as there is a lack of regular players now. Actual high scores are probably no longer recorded by Cheetah Mobile. Actual previous records for each challenge can be found on their pages in this wiki. If you can still beat any previous records, you are welcome to write it down on those pages, as long as you can provide video proof.