Question: [solution]iPhone music suddenly not in Itunes
So I suddenly found that large amounts of my music was missing from my iTunes on my computer, but not my iphone. When I hooked up my iphone, the computer's iTunes only showed even less songs on my iphone, so syncing wouldn't work!
After some fussing, I checked my iCloud account, and re-signed into that to be sure: and THAT did the trick! MY music is showing on both my iphone and iTunes again! (My iCloud account prob got signed out of during an upgrade.)
So make sure BOTH iTunes and iCloud accounts are signed into!