iPhone and iTunes Apple Music sync problems

Devices: iPhone 6+ iOs 8.4, Mac 10.10.4 and iTunes 12.2.0.145

Whenever I add a specific album to "My Music" on my iPhone, all the songs are added normally, but when iTunes on Mac automatically syncs, it syncs only few songs...(which is weird) then I find the same album on iTunes and try to add the missing songs and nothing happens...

If I try to add the full album to My Music (+ sign) on iTunes, just the same few songs are added, and the same few songs are synced to iPhone.

Anyone had the same problem? Any solution?

Ps: Tried to delete everything, start all over, and same thing happens to the same specific album. All other albums are OK.