Hey there! I tried replicating the issue on my end, but I couldn’t see the message – just your site being displayed correctly.
I think your firewall might include a rule that catches all Jetpack Monitor requests (either by looking at the IP, or at the User Agent), and serves a custom response to the monitoring agent, with the body “Hi Jetpack! All systems go.”
This tricks our Agent into thinking that your site is always up, making the agent completely useless.
Could you try disabling your firewall or reaching out to your hosting provider and ask them if they have such a rule in place?
If that’s really happening, you can just disable the Monitor feature from your site. You can do so here:
https://wordpress.com/settings/security/
Once you’ve done so, please let me know the name of your firewall or host; I would then reach out to them and see if we can work together to remove that rule from their system and thus have Jetpack monitor the site itself, not a special response set up by the firewall.
Moreover, it’s also possible that your host or your caching system is caching the firewall response and then serving it to regular visitors. That wouldn’t be a problem if the first problem was solved (since the response the monitoring agent would get would be the same as the visitors), but in this case it is a problem. You would consequently have to make sure Monitor responses are never cached in your system.
Could you run some tests and let me know what you find? Thanks a lot!