Hi @Roger Jou, we've also encountered the same problem in HTMLtoPDFConverter. In our case, the root cause is the Content-Security Policy of the application is turned on. Please refer to this thread.
We tried all the solution to fix the CSP issue of the extension but with no luck.
As an alternative extension, we use UltimatePDF and so far we are not encountering CSS formatting problem even if the CSP is turned on.
Hope this helps,
Thank you