Hi @Michael_Lande ----- Thank you for the report and sharing your feedback, both are appreciated!
I am not sure if you have given our knowledge base a look yet but we have good documentation on why some file may not show up in ROON that could help in your troubleshooting 
Moving forward, to help aide in my assessment of this behavior you are experiencing, may I kindly ask you to please provide the following information:
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In regard to the missing content, can you verify if any of the media is DRM protected? Downloaded content from iTunes is usually DRM protected.
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Can you confirm if you have “show hidden albums” enabled under the “general” tab found in settings?
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If you were to search for a missing track via it’s “path” are you able to locate any of the missing content? More information on this process can be found: here.
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You’ve also made mention of the following:
" I have selected “Prefer File” for every option shown. When I am browsing albums, the artist names correctly show my tags. However, when I browse by artist, artist names are showing Roon’s tags."
Can you provide me a screenshot of:
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Your metadata preference highlighting your settings (i.e “prefer file”).
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The album browser window that correctly displays the artists name as shown in your tags.
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The artist browser that shows the artist names from Roons tags.
-Eric