ServiceNow has botched a root certificate upgrade, service disruptions worldwide

https://support.servicenow.com/kb?id=kb_article_view&sysparm_article=KB1700690

Unfortunately you need to log in to their support portal to see it, because it's always a great idea to gate information behind logins when you're experiencing a major service degradation.

The gist is they had a planned root certificate update for the 23rd, something didn't work, so now the cloud instances can't talk to the midservers, plus other less clear but noticeable performance and functionality issues.

If you're impacted and want to be kept updated, you need to open a case on their support portal and wait until it's added to the parent incident, as they're not at the moment proactively informing customers (another great idea).