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Make sure iTunes is up to date.
On your iPad, look at your settings in Music. Disable iTunes Match, if it's enabled. If you use iCloud Music Library, disable that too. Now try syncing.
Connect your device to the computer.
In iTunes (computer), select your device. Click Music below it, uncheck "Sync Music", then choose "Sync" or "Apply" at the bottom.
Then checkmark "Sync Music", and sync/apply.
Let iTunes finish syncing, unplug your iPad and take a look at your music.
If that doesn't help either, go to Settings - General - Reset on your iPad, and select "Reset Network Settings". Connect your device to the computer. If you get the popup whether or not to trust the computer, select "Trust...".
In iTunes, select your iPad, go to the Summary tab, scroll to Options, and checkmark "Manually manage music and videos". Then try syncing again.
Hope that helps.