It's cause of Spotify
So we all know T1419 is now TFN, however this bugs on Spotify.
T1419's verefied account was renamed to TFN, so all your saved songs are still in your playlists, but just a new name Makes sense
However (!) when you click on TFN's verefied account, only the Japanese songs show up. The Korean songs are still there, just not shown up anymore, wich is strange.
But, now it comes (!) if you search for the Korean songs, they are shown on someone else's account who is an unverefied artist who also gets called TFN.
So yes all the songs you saved are still on the original account, however the rederection to the name TFN seems broken and direct the Japanese songs to the right account, but the Korean songs don't if you search them outside of your own playlists.
It's strange and I hope MLD can get this fixed.