I could not find the issue. Aspose.Cells follows MS Excel standards and specifications when parsing or rendering HTMLs. I did test using the following sample code, it works fine:
Workbook wb = new Workbook();
Worksheet ws = wb.Worksheets;
var cell = ws.Cells[1, 1];
cell.HtmlString = "<html><body><p>This text is normal.<b>This text is bold.</b></p></body></html>";
Workbook workbook = new Workbook("e:\\test2\\output.xlsx");
string tmp = workbook.Worksheets.Cells[1, 1].HtmlString;
<Font Style="FONT-FAMILY: Arial;FONT-SIZE: 10pt;COLOR: #000000;">This text is normal.</Font><Font Style="FONT-WEIGHT: bold;FONT-FAMILY: Arial;FONT-SIZE: 10pt;COLOR: #000000;">This text is bold.</Font>
It looks the above output is ok. Even then, I pasted the above html output string by creating a file and save it as “.html”. It works fine when I opened the HTML file into the browser, it shows correct output too.
Could you share your Excel file and sample code (runnable) to show the issue, we will check it soon.
PS. please zip the Excel file prior attaching here.