You are right; some hyperlinks (fields) do not work during converting this Word DOC document to HTML Fixed file format. We tested the scenario by using the following C# code of Aspose.Words for .NET API on our end:
Document doc = new Document("C:\\temp\\link_sample\\test_link01.doc");
HtmlFixedSaveOptions htmlFixedSaveOptions = new HtmlFixedSaveOptions();
htmlFixedSaveOptions.PrettyFormat = true;
htmlFixedSaveOptions.ExportEmbeddedCss = true;
htmlFixedSaveOptions.ExportEmbeddedFonts = true;
We have logged this problem in our issue tracking system with ID WORDSNET-22058. We will further look into the details of this problem and will keep you updated on the status of correction. We apologize for your inconvenience.