Getting 500 errors for no apparent reason

[user4046]

We have been using Cloudflare for a long time without any issues. Several days ago www.estateblock.com started to give 500 error (consistently). The first reaction and that there is something wrong with the website, but digging into that more, it looks like the server is not even getting hit by the requests.
Also, another subdomain (https://m.estateblock.com/) works.

I found this post from a while back that mentions that there is a rare case of that might happen.

What could be a reason for it? How can we debug it?
There is literally nothing is our access logs or error logs.

[sdayman]

Does it work (with HTTPS) if you toggle the DNS entry to DNS Only and give it five minutes to take effect?

[user4046]

It is on DNS only right now. I was trying to play with it from the very beginning.

[sdayman]

That’s definitely a server issue:

[user4046]

Oh wow!!! Apparently, we got hacked!!! Apologies for bothering