Is there music on your device that isn't in your library? Have you enabled iCloud Music Library in iTunes yet? When you use iCloud Music Library as part of iTunes Match or Apple Music the idea is that you load up the iCloud Music Library from iTunes, and this entire library then become available to any of your devices for streaming or downloading. Anything stored only on the device when iCloud Music Library is enabled might potentially be removed from it, but if it is present in your main library then there will be a streaming link so that you can access the matched or uploaded version.
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