Links inside of the Jira email notifications from issues.jenkins-ci.org have been broken for me for a few days now due to HSTS errors on https://url1399.jenkins.io/. Here is one of the links from one of the notifications as an example (it should go to JENKINS-42214).
The error that Chrome shows is NET::ERR_CERT_COMMON_NAME_INVALID. From a quick look at the cert chain, I think the common name for the cert on that site is *.sendgrid.net, but I might be looking at the wrong one.
Let me know if you need any other information from me to help diagnose the issue. For now, my workaround is to just navigate to JIRA directly instead of using the links in the notifications.