In order to fix this bug I've been trying everything I could find on the internet. Basically whenever I try to sync music or videos from iTunes to my iPhone (they have both the latest version) and during the last step of that, iTunes would randomly stop just few songs from the start and it would wait until sync timeout.
Then I've also tried to export the songs with CopyTrans Manager which is a 3rd party tool similar to iTunes, but I get the same error: sync -> then stop at a random song -> app timeout.
Then I've tried an app from the store called PlayerExtreme, and I've tried exporting song to that using iExplorer but I still get the timeout.
The only error I got was that my iPhone disconnects during the process, which is weird since I've tried using 2 different USB cables (both original) and both of them randomly disconnect during the sync and they both reconnect few seconds later.
Other stuff I've tried:
- toggle sync / no sync music from iTunes
- sync only selected music and videos
- manually manage music and videos
- delete all music from my iPhone
- resetting network settings (someone got it to work with that)
- airplane mode
I've also read it could be because of duplicate songs in the library but I'm sure I don't have any duplicate song.
Also I'm not a iTunes Match customer.
EDIT: I get this error quite often : "This accessory may not be supported". Especially when I'm charging it on my PC and the battery percentage gets closer to 100%. I got the same error with both my 2 original USB cables.
EDIT 2: IMO it's either an iOS 8 bug or some kind of weird problem with my USB ports.
Best Answer
Changing USB port fixed my problem. At first I was using an USB 2.0 port on my case, then I moved my iPhone to the USB 3.0 port of my motherboard and it worked.