Missing music on iOS devices compared to library in iTunes

Does anyone know why an entire iTunes music library wouldn't sync to iPhone & iPad when that is the setting I've created when the devices are connected to my Mac? I have 4329 songs in my Library and have Sync Music 'entire music library' checked off with my settings during syncing. It's 'anticipating' 4224 songs (# listed beside Sync Music) yet I'm only getting 3520 songs to sync.

Any help would be greatly appreciated. This is a NEW issue since the newest version of iTunes has been released.

Thanks in advance to anyone who might have a solution.