Empty sitemap error in search console after moving to https with Wordpress

I'm on Wordpress 4.8.1, with Yoast SEO sitemap.xml enabled. I recently moved to https.

After submitting the sitemap to search console it says the sitemap is empty and does not contain URLs. But I can see content of the page in browsers and google bots can crawl it too.

I submitted to search console http, https, www and non www domains. And I get this problem on all the versions. When it was just http I had no problems with the sitemap.

I 301'ed sitemap_index.xml to sitemap.xml

My robot.txt:

User-agent: *Allow: /Sitemap: https://giessedati.it/sitemap.xml

I used some validator and all say the sitemap is valid.I tried uninstalling-reinstalling Yoast Seo and other sitemaps plugins with no results.I removed caching plugin (W3 Total cache) and cached content of the site.