There is a few years old small website with very few pages (~5), which were indexed and ranked by Google. A few days ago 4 of those pages disappeared from SERPs and Search Console gives me 404 Not Found errors despite the fact that the pages are up and running. I didn't do any changes in header's crawler related meta tags and robot.txt neither.
Tried to submit a sitemap.xml but it gives me 404 error for that too.
What causes this problem?