Full automatic Itunes synchronization impossible for a brand new Ipod touch 5th generation

Question

Hey all,
I bought a brand new Ipod Touch 5th generation which won't synchronize my whole music library through Itunes (very latest version of the app).
The ipod runs IOS8 and the mac mini runs Yosemite latest version.
I already had issue synchronizing music the very 1st day I had the Ipod touch. As a result, went back to the Apple store for changing it for another device, thinking the Ipod was faulty, which Apple accepted and changed my device for a brand new one.
Since then, still unable to synchronize the full music library through itunes. I performed several full resets both on the mac mini and of the Ipod touch with no success. The synchronization seems to run fully normally with no warning pop up saying it failed or whatsoever and the sync process is very very long. But once done, my Ipod remains empty with no data at all.
The weird thing is that Photos are fully synchronized with no issue at all.
I contacted the Apple assistance who argued that my music library might be faulty and have corrupted files in it. So I cleaned it up, suppressing some files I had in double etc.
BUT still, no success, I had to go through the entire library to sync manually, but even then, I was able to have on the device, only half of the library, i.e. around 25 go. once the ipod display 25 to 30 gb remaining, it won't sync no more files.
Although I cleaned up the entire library and reset both devices hundreds of times, I have no clue why even manually, I'm completely unable to have my whole library automatically sync.
I spent hours on the phone with Apple assistance to get some help with no success so far. I even re-installed Itunes completely, still without any result at all.
I was only able to upload on the Ipod only half of the music library, and there are still 25 to 30 GB space remaining on the ipod and 20GB of music to be uploaded.
The automatic sync process always fails any time I try to run it, except for the photos, books etc.
I must say I also have an 160 GB Ipod classic with which I never had any problem so far, and which fully sync my whole library with no issue at all.
I read on the internet that some other users of IOS8 are accountering the same issue with itunes.
COULD SOMEBODY PLEASE HELP, I'M DESPERATE, given the price of the Ipod I really do regret I bought something that does not work properly. Quite disappointed

Answer 1

Yes the system just keep sync as everything is normal, but then no song is actually uploaded to the ipod.
And the remaining space bar shows the ipod's empty.
the automated process will just keep sync as if normal and the last step saying 'applying the modifications" just keep going on and never ends.
I was only able to upload manually half of the albums, all songs comes from different sources; ripped from CD for great part, but also downloaded from the internet from trusted websites.
All songs play normally through Itunes on the Mac Mini.
But then when trying to sync the whole library automatically, nothing happens and I only get tags of the different albums, as if there, but actually it won't play none and the Ipod player just keep skipping as if no musical data is there.