Sync to iPod completes but not showing as songs

[sullydks]

Hi
Been synching to iPod successfully via MM for many years.. ie via MM to Ipod 160Gb Classic.
But now... if I select all the playlists I need to sync, (about 13K tracks), which still leaves about 10Gb less than full disk (so I have the space), the sync finishes (MANY HOURS later) but upon disconnecting the iPod and there are no Songs. The space is used. The MP3 files are there (if I browse the disk) but the space is marked as 'other' in the iPod ABOUT display. Not songs.
Rebuilding device DB, doesn't appear to work. This just gets stuck around track 100 or so, (it varies) of 13,000 , and never moves on. I've left it for well over an hour or more to be sure. But the counter just sits there 'stalled'. Task Mgr, shows some CPU activity from MM process but the counter never increases.
I've restored the iPod (via iTunes) and started from scratch - no joy. Same as above.
If restore, to zero, and sync from MM to iPod with say just a handful of playlists = 1000 or so songs.. No Problem. All is good.
But the full sync isnt. It takes an age to sync 13K mp3, since the files are on a NAS MM on the laptop so re-starting it all is becoming tedious.
I leave it overnight.
Any suggestions.
Any thoughts anyone ? anything obvious I may have missed...

W10, MM 1914, ethernet connection to 'switch' to NAS. Network comms are good. Restored iPod to latest avail version for the 'classic'.
iPod Disk OK, battery fully charged and charges fine.

[Lowlander]

Which version of MediaMonkey?