arbiscuit Said:
"Unable to re-download a song in iTunes on my iPhone.: I don’t quite know by probably a quarter or the songs in my library got hidden. I was able to unhide them. Thank you very much!”
———-
You are welcome.
My Thoughts are that Either:
A. You mistakenly hid these
OR…
B. Someone else did so
So, Secure your Info;
Being Login of high concern, (A)verify your devices, and (B)secure your account. Open a new eMail addressee and use that for your Apple ID.
1. Verify your Devices:
Verify that all devices are logged in to your account, by using this link: Check your Apple ID Device List to See where you're Signed in - Apple Support
then...
2. Modify your Credentials:
Having been stollen, someone lily has your credentials. So, by all means, modifying them.