Can not submit a sitemap in the search console

I manage a few sites and one customer reported that his web traffic had decreased and his home page was no longer on Google.

The site has been running for 10 years without any problem.

I recently added an SSL certificate and using the web.config file, I configured it to redirect.

In the search console, only http was listed. I've therefore added https, then tried to submit a sitemap.xml file, but the message can not be read even if you can see it correctly in the browser. Additionally, when I try to run the Mobile Friendly test, the message "The page can not be reached – maybe the page is not available or is blocked by the robots file." .txt ", even if the robots.txt file lets everything pass. It bothers me and affects their ranking.

Can any one advise what this could be?

You can see on the image that the problems have started recently and that the home page is listed as excluded and "currently unindexed". No idea why.

Would this be the http / https redirect?

This is the configuration of the web.config file



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