In general for fastest response be sure to email us at https://www.microsystools.com/home/contact.php
Please also include a link to your website in your email.
Default settings will include .html in XML sitemaps, but it could be a whole range of issues: Javascript links, MIME content issue, canonical issue (your .html pages point to another page) or something else.
Solution is usually to tweak settings. Email us and we will be happy to analyze the problem, explain it and give your a working project file
Update: Problem resolved over email
