This has appeared in the Message center - "We're retiring the classic Office 365 service health dashboard":
"In March 2017, we completed our work to bring improvements to the new service health dashboard and started rolling it out to all customers as the default experience. We also gave admins the ability to switch back (using a link) to the classic experience.
This classic Office 365 service health dashboard is being retired
"Starting at the end of this week, the new service health dashboard will be the only experience. If you're trying to reach the old dashboard, you'll be automatically redirected to the new dashboard."