For me, I have never had so many issues with an iOS until iOS 8 was released. I don't remember ever having any synching issues with iOS 6 or iOS 7. I have an iPhone 5
There are pages and pages of user having synching issues with iOS 8 and iTunes, removing songs and artwork and showing incorrect available data, if you restore your iPhone you will get back all your songs and artwork but as soon as you synch your iPhone to iTunes again it will start removing songs and artwork, it's a vicious cycle. I restored and got back all my 5,000 songs I have in iTunes so my phone is finally showing all my songs and artwork but I will not be synching my iPhone to iTunes until Apple issues a fix for the synching problem.
https://discussions.apple.com/thread/6541755?start=0&tstart=0
There are pages and pages of user having synching issues with iOS 8 and iTunes, removing songs and artwork and showing incorrect available data, if you restore your iPhone you will get back all your songs and artwork but as soon as you synch your iPhone to iTunes again it will start removing songs and artwork, it's a vicious cycle. I restored and got back all my 5,000 songs I have in iTunes so my phone is finally showing all my songs and artwork but I will not be synching my iPhone to iTunes until Apple issues a fix for the synching problem.
https://discussions.apple.com/thread/6541755?start=0&tstart=0