Thx for the detailed explanation!
But actually I always backup via itunes only
And I did these backup & restore many times before with no problem
Just dunno y it doesn't work this time
So I guess it's caused by some setting about iCloud on my 6
Okay, I understand.
Where are you trying to restore your sync from? iTunes or directly on your phone First-Use screen when prompted to choose a recovery option?
If you do try from your phone, try from iTunes by plugging it to your computer while setting it up and vice versa if you are doing the restore from iTunes.
iTunes may have missing files or incomplete data to recover that your phone don't have.
(If you always backup from iTunes, it would normally show you the latest backups made with any other iOS devices that are compatible with the device plugged in to the computer)
If that still doesn't work, you may try the following.
(
The following option will once again erase your data)
Unplug your phone (
the 6S has to be restored, not your 6 that contains the data, just to avoid confusion) it if it's plugged in to any computers.
Enter DFU mode or Recovery mode by pressing the home button and the power on button for about 8-10 seconds and release the power on button while keep pressing the home button.
If your phone restarts with the Apple boot logo, the procedure was not recognized by the phone.
If you see literally nothing (like your phone is off) or an icon with iTunes, your phone entered respectively DFU mode or recovery mode.
Plug it to your computer, and iTunes will tell you it has recognized a phone in recovery mode and it has to restored before being used.
iTunes will search for the latest firmware compatible with your model, and restore it.
You may retry to restore your data.
Considering you restored your phone, if it says the sync restore is incomplete, it is most likely that it is corrupted.
(All of this supposing that your shiny new iPhone 6S may have software failure, and that an all new firmware downloaded from iTunes may fix the problem)
UPDATE -> If you backup your 6 with iOS 9, and that you're trying to restore onto your 6S that may run iOS 9.0.1, it may not work due to the fact that your backup is on an older version of iOS.
I really hope you'll find a fix to the problem, and hope that helps a bit
