Compiling: why italics to underline?

Why does Scrivener compile italics to underline? This occurs in any format

Do you have it turned on in the Transformations of your compilation settings? (File/Compile, then double-click a section layout and look under Transformations)?

Thanks but that’s not the issue. It’s bizarre, but my entire project is locked in blue-underline hell

What happens if you cut a paragraph with italics in it, use the Paste and Match Formatting command to paste it back in as plain text, fix the italics that will have been dropped, and then compile again?

That’s surely not a solution to be clear, but it might help troubleshoot what the underlying issue is.