When the module generates a new sitemap.xml file and notifies the search engines (Google and Bing), it uses the HTTP protocol.
Both Google and Bing use HTTPS for all their services, so they respond with an 301 HTTP responde status code, which makes the module send the notification again to the new URL.
The module should use HTTPS protocol both for Google and Bing.
This issue is related to the issue #2907878: Use HTTPS protocol when notifying search engines, but in this case it's over the 8.x-1.x version.