iTunes/Music.app Missing song

Hi all, I have this very confuse isssue.

1.

I have two albums of same artist. Album "X" with song called "Y", and album "XX" with same song "Y", same song name. Example: 1st is "normal" album, and the 2nd one is "Best of ..."

When I add album "X" to "My music" on iPhone, in iTunes on Mac I can see this album and song "Y".

When I add album "XX" to "My music" on iPhone, the song "Y" is contained only in album "XX", and from first album "X" this song has been deleted.

2. If I delete albums in iPnone's My music, albums are deleted from all devices, but If I delete albums in iTunes on Mac, albums are not deleted from iPhone and other devices.

I've tried delete all songs from iCloud music library, but no success :/

Can anybody help?

Tnx