Some of my sites are showing that they are down

Yesterday I got those e-mails

DOWN alert: appears down
Hi +++ Pitts,

Our systems have detected that your site - - went down on Nov 28, 2018 1:51am and is returning "Request timed out.."

We recommend that you visit your site to confirm the problem.

If your site is up and now running smoothly, just ignore this email. You can find out more about what went wrong here.

But the website is ok and accessing.

When I go to HUB > My website > Uptime, the service shows me the site is down since yesterday, I tried to refresh, also disable and enable it again and no luck.

But if I go to Hummingbird plugin > Uptime > Downtime, it didn't me show me any downtime Yesterday.

Can you help me?