I believe we need fsPath in this case because it normalize path on windows.

If the preview is not working for unc paths, first try debugging into provideTextDocumentContent in previewContentProvider.ts to see if the document is loading properly or not

Why we need the normalize path? For the markdown extensions? Or for the Uri internal behavior?

provideTextDocumentContent is not called. Because Error occurred at URI._validate in process of getMarkdownUri before it.
The Error is caused by UTC path is regarded as wrong URI. So, this error has been raised on other TextDocument events too.

Thanks @tomoki1207

We need to normalize the path for scroll synchronization. I believe this normalization already happens downstream in provideTextDocumentContent, so let's see if this change causes any regressions. It should be in the next insiders build

Works fine on 1.13.0-insider.
Thank you.