Always Online isn't Always? What's Wrong

I have just had several sites go down due to 503 errors or something like it. My VPS isn’t responding. I have “always online” on each of the sites however they are not resolving to the cached version that they should be. Why is that? Some I’m getting a 522 error. It differentiates.

Always online currently triggers for status codes 520-527 . Refer to Always Online · Cloudflare Cache (CDN) docs

Why doesn’t it include the other 500 codes? It sounds more like “Mostly Online” rather than Always Online.