This is just about 100% restored.  
You can get status here.

https://nintex.status.io/pages/incident/566925105401bb333d000014/5f5b7840c72b4804c0c193ec

Some of our customers with older versions are getting the attached error. Would that be related to this same issue?

I would guess yes- that specific URL is on the domain that is down for us. We havent gotten that exact message, but I would say its the same.

Some people have reported it working again. If I can get anyone from IT to experience this I'll ask them to inspect the cert and see if its updated. Those take a while to propagate and might explain why some people are back online and some arent. 

I did a DNS flush and I can see the new certificate - thank you! tested and working