Why is it showing a question mark in my ITunes library instead of the song being under the correct letter?

I have this same issue on my iPhone SE. On the phone in the main Apple music app, under Library, under Songs, the bottom of the list (below songs that begin with "Z") is a "?". Under the "?" symbol, I have about 125 songs listed rather than being listed under the Artist as they should be. The issue seems to be tied to entire albums. These are all from legitimate, purchased CDs (not copies) ranging from 1-10 years old that I loaded to my iTunes library. A variety of artists are affected. However, only some of the albums from those artists create an issue, so it's not just tied to the artist. The CDs are produced by a variety of music companies, so the production company is not the issue.

I checked all of the album and song data particulars to ensure I didn't have some odd characters in the naming or have an odd button checked. Everything seemed to be listed correctly.

Finally, I resolved the issue by thoroughly deleting the problematic albums from my iTunes ("send to recycle bin"), re-syncing my phone, and ensuring those albums/songs also no longer appear on my phone under the "?" (or anywhere else). Then, I re-loaded the CD to iTunes (ensuring the "compilation" button was not checked before I did so). I re-synced the phone and those albums now correctly appear under the artist name.

This will be a time-consuming fix, but it's the only thing I could get to work. However, since I don't know what causes it in the first place, this will probably happen again with future CD album loads.

Hi RockSolid93,
Thanks for using the Apple Support Communities. It looks like no one has responded yet to your question. If you could provide the following information, it may help the community respond:
1. What is the exact screen that you are seeing, and where are you seeing it? Can you describe in more detail what you are seeing? Is this in iTunes on your computer or in Music on your iPhone? Are there any alerts or error messages?
2. How long has this been going on? Was it working successfully previously? If so, has anything changed recently (new network location, new app or OS update, etc)?
Cheers!

Go to your computer's iTunes library. For each song that is listed on your phone under the question mark, click that song on your computer, then click Edit (at your toolbar), then click Get Info, then uncheck the Compilation box, then click OK. Once done, re-sync your phone to your computer, The songs on your phone that were previously listed under the question mark are now where they belong.