iPod Touch very slow processing large song collection

Well, this is very frustrating. I decided to go ahead and eject the iPod, then reconnected it. This appeared to restart the transfer process for the playlist. After it appeared to transfer successfully, I transferred another 7 or 8 playlists. All went well until the final playlist I attempted to transfer. Now, the iPod showed no songs or playlists at all (even though iTunes still reported them existing on the device). I ejected and reconnected the iPod again. Now a message came up stating that it was syncing, step 4 of 4. Eventually this ended.

However, now the iPod only shows that it contains a hundred or so songs that I bought from iTunes -- not the thousands of other songs that I had transferred (most of my collection is imported from CD's). The iPod also isn't showing any playlists.

Is there anything I can try doing, apart from restoring the iPod to factory defaults yet again and trying all of this over? It certainly doesn't seem to do a good job transferring songs and playlists when a large collection is involved. Are there any third-party apps I could use for these transfers?

Thanks but, as noted in my first message, the computer I'm using to work with the iPod Touch is a Macbook Pro (running Yosemite).

I've now gone through this pattern of events a couple of times -- I transfer songs/playlists to the iPod, everything seems okay, then I want to transfer some new songs or a new playlist, and the entire song database on the iPod seems to get hosed-up. It pretty consistently arrives at the same state -- iTunes shows the iPod as containing all ~7,800 songs, but the iPod only shows that it contains and will play the couple of hundred songs that were purchased from iTunes. I've tried restoring to factory settings and redoing all this a couple of times, and the error keeps happening.

If there aren't any other procedures or tools to try using to manage the song/playlist collection, all I can think of doing is putting a far smaller number of the songs onto the iPod and see if it can handle them better.

This is discouraging, because my old 160 GB iPod Classic handled all ~7,800 songs beautifully for years without any of these errors. I'd still be using it if its disk storage hadn't gotten dodgy and started causing song dropouts.

Here's a bit more.

I reset my 64GB iPod Touch to factory settings, used iTunes on Macbook Pro to transfer 51.5GB of songs to it; this appeared to go okay. I then transferred a 243-song playlist to the iPod; all of the songs on the playlist had already been transferred. After this concluded, the iPod showed only songs purchased from iTunes, none of the other songs I'd transferred. Interesting, iTunes reported that the iPod was now 43GB over its allotted size.

Next, I reset the iPod Touch once more to factory settings. This time I disabled wifi, Apple login, etc, just to simplify things and make it a simple file storage device. I transferred a much smaller selection of songs (a few GB) to the iPod; this went fine. Next, I transferred the 243-song playlist and some other playlists. These transfers seemed to go fine; playlist songs that hadn't yet been transferred were copied to the iPod. Everything seems stable.

So, my takeaway is that even if iTunes says the iPod has 59GB free, it isn't really feasible to store 51.6GB of songs on it. It seems as though the software used for transfers needs a lot of "scratchpad" space in the iPod's file storage. Over the next few days/weeks I'll try very gradually increasing the number of song files I keep on the iPod, and see how much it can actually handle.