First check one of the music files and see if it is actually 0 KB or if it still has its normal file size.
If these files are in OneDrive, sign in to OneDrive on the web and check the Music folder there. If the files still have their data online, you may be able to download them again or use Version History to restore an earlier version.
Also check the OneDrive Recycle Bin in case the original files were deleted or replaced. If you have Microsoft 365, Restore your OneDrive can also roll back file changes from the last 30 days.
I would avoid copying or overwriting the empty files until you confirm whether the original data is still available online.