Slash (/) characters in file names gets converted to a semicolon in the file name field

[Florian]

It looks like it's the classic colon issue with macOS and Finder. Here is a little more context and explanation to it:

Why is MP3 Tag Replacing Chars

It's a thing specific to macOS and Finder. The filenames actually use the colon character : (as displayed correctly in Mp3tag) but Finder does some auto-translation into the forward slash /. You can verify that yourself by opening Terminal.app, navigate to the Disc 5 folder, and use the command ls -la to list the folder contents. More on that here: