Another thing I noticed was that:
- my sitemap was named like: 'example.com/sitemap_index.xml'
- during setup, it was recognized properly
- during crawler it seems it wasn't been used, then I went o check the config
- there was a "custom sitemap" URL there with "example.com/sitemap.xml" on it
So, it seems that, the setup it not working properly and the crawler assumes it is named like "/sitemap.xml".