XML Sitemap not showing any entry

https://semperplugins.com/documentation/all-in-one-seo-pack-xml-sitemap-404-nginx/

@ozzielisting
That isn’t the url for All in One SEO Pack’s sitemap, not by default anyway.
Unless you changed it, something else, for instance another SEO/sitemap plugin (even one that used to be installed) is changing the URL to one where no sitemap exists.

I will follow the link provided for the instructions. But how did it happen it works perfectly fine recently?

If it suddenly stopped working and used to work fine before, then you might want to check if you have a theme or plugin conflict going on your website.