*.nelreports.net is a Microsoft domain. Several certificates used on the subdomains of this domain expired last week.
There is no security impact or end-user-impact of the certificate expiration -- Basically, the browser will be unable to submit Network Error Logging reports until the certificate is corrected. Network Error Logging is a HTML5 feature to allow site owners to discover network connectivity problems. https://developer.mozilla.org/en-US/docs/Web/HTTP/Network\_Error\_Logging
Your security software is just announcing "Hey, this certificate is bad", a fact that the browser already was determining on its own, and to which it responds by not connecting to the server in question. The security software provides a redundant warning -- the browser will not use connections with expired or invalid certificates.
The subdomain names are random strings of characters with no particular meaning.
The relevant team has been notified about the certificate expiration and will correct the issue.
