disappearing music on ip6

i have ip6-128 ios8.2 with about 90 gb of music on it. (the music is ripped from my cd collection and transferred from pc by itunes and not downloaded). for some unxplainable reason all of the music disappears from the phone when i sync with itunes and reappears hours later. its become so annoying that i cant load any new music or delete old ones because i end up loosing hour to fix this thing. while the phone is connected to itunes, the phone appears without any music, but can see all music on itunes. when you double click it gives an exclamation mark and does not play.