5G iPod Touch won't sync with iTunes 12.3.0.44

Since the last few upgrades to iTunes and iOS, I'm having serious problems syncing my iPod Touch to my iTunes.

Got the latest versions of iOS and OS X on my device and iMac, as well as the latest iTunes.

iPod Touch is set to sync over WiFi. iMac and iPod are both connected by WiFi to an Airport Extreme router which is placed less than 2 feet away from the iMac.

Each time I try to sync the iPod over WiFi, the process aborts after a while with the error message "iPod was disconnected".

So I connected the USB cable and tried to sync my iPod ... and got the error "iPod cannot be found".

The iPod shows up in iTunes ... so these error messages are just incredible.

In other words, syncing isn't working either by WiFi or by USB connection.

This is beyond frustrating.

Has anyone else had the same experience?

The only way I can get it to work is to restart iTunes and power off the iPod - several times, until it eventually syncs up. This is not the way it should work. Not with the latest operating systems.

Suggestions on how to fix this problem are very welcome.

Thanks