iTunes can not find music anymore after changing IP address of NAS
As I can't comment on post so it comes as an answer:

Are your iTunes library accessing the NAS as a shared library or as imported files?

If it's imported files the "file location" stored in your iTunes library still contain the old IP. Changing all of these will take forever and I do not know if there is any application or plugin that can batch-change them. Deleting all files and importing them again might be the easiest solution to your problem.

You can see the songs location in the Get info -&gt; Summary -&gt; "Where:"