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No matter what kinds of changes you're making to your website, it's better to put up a coming soon or under construction message instead of just showing people some generic error saying the site is unavailable. I
I agree with that, yes. In this case, even cloudflare shows the exception with an HTTP 502.
There is actually only one situation here where this is not technically possible:
If the Sinbad team has to move the entire server infrastructure from one operator to another, then they may no longer have access to the old infrastructure and therefore can no longer place a message there. For this to happen, however, the old operator must have simply turned off the services, and to be honest it doesn't look like that to me either.
Nevertheless, I assume that the infrastructure will soon be available again. A statement from Sinbad about how long the downtime will last would of course be very nice.
If the website owners have control over the domain, there is no situation that prevents them from creating an informative page about maintenance.
I honestly don't think there is any problem with the service, because so far (it seems) no one has yet complained about any loss of funds.
Now I have to admit that they are showing a management failure in this maintenance process. Let's see what happens in the next few days.