Only 1 of many domains unreachable in two cities

I have a few domains on my server and I can reach all their websites. I was alerted that one of my domains was unreachable from Finland and after checking with siteuptime.com and alertra.com I see that that single domain is unreachable from Chicago and LA as well.

This domain is on the same server as my other domains, and is using the same registrar.

Where would the problem lie that would cause this one domain to be unreachable for the past few days?

The domain had resolved to our server a week ago, and the nameservers for the domain have been set correctly.

I checked MY nameservers in Registerfly and it claims they are not registered. According to LiveChat they are set to the right IP addresses (implying they are set correctly). I can not ping my nameservers (if they were down why is only one website unreachable in only two cities?).

 

 

 

 

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