Uptime not working for newly-added websites

I have several websites on my HUB and am using Uptime monitoring. Recently I added two more websites to my dashboard, however when Uptime tries to ping the new sites it seems to fail and reports that my websites are down. I have confirmed that the sites are accessible. Interestingly my other sites that were already in my dashboard don't seem to be affected.

I have already tried to log out and back into my WPMU Dashboard and have gone to both of the offending websites, logged in and refreshed the pages. I even uninstalled/re-installed the Hummingbird plugin, but to no avail.

The issue seems to be with the WPMU HUB because when I log into my website's admin backend and view the Hummingbird Uptime tab it shows my website as being online and available, however, back on the HUB it still shows it as being down.
Your assistance with this matter would be greatly appreciated.