Uptime reporting sites as down when they're not

Uptime is not able to contact one of my servers, sites are marked as down but they are up.
I'm being alerted to all of my sites being down, however they are not. They are all on the same server and I suspect I got a little too carried away with the firewall and may have blocked the IP address the uptime monitor pings from.

I checked it and I'm not seeing any attempts from these IP addresses to access the server. Unfortunately I can't whitelist by user agent.