Timeout from status page

When I go to the status page in the admin panel I get an error popup after a long time.
The Nginx logs show that the miab backend is giving a timeout.
I was looking for logs that could show what is going on, but I could not find any.

The box hosts 20 domains or so - each with multiple subdomains, custom dns, multiple users, etc.

Any idea for how to debug this problem ?

There might be a timeout involved due to the many (most people have less I think). I believe it is set in /usr/local/lib/mailinabox/start at 630 seconds. But please verify, as this is over 10 minutes!
How long does it take for the timeout to happen?
You can get the mailinabox logs by sudo journalctl -u mailinabox maybe there’s something in there.

Looking into this a bit more, there might also be an nginx timeout involved, like Module ngx_http_proxy_module
But I’m a bit out of my depth here, maybe someone else could chip in on that?

It seems to be the nginx timeout because I can get the correct result by using curl directly on the command line of the box.
I will check the journal logs to see if something is blocking it

checked the time it takes and this is what I get

real    2m2.997s
user    0m0.006s
sys     0m0.027s

I used this command:

time curl -s -d POSTDATA --user $(</var/lib/mailinabox/api.key):

It seems like a lot of the lookups just takes a long time. Maybe some of the checks should be split out - like e.g. te spamhaus check

proxy_read_timeout defaults to 60 seconds, so you’re probably right about the nginx timeout.
Perhaps you can try to edit /etc/nginx/conf.d/local.conf? Look for the line
proxy_pass;, then paste proxy_read_timeout 300s; after that.
Restart nginx sudo systemctl restart nginx and try again?