On Friday, December 11th, from 1500 and 1700 CST (2100 to 2300 GMT), the Cloud Operations team will be applying updates to the EU - Enterprise One London Datacenter Power BI Report Server farm. During this time all reporting will be unavailable for customers v15+.
This is just a change to the authentication code and not a change to the version of PowerBI running on the farm.
If you do experience any issues with existing Power BI content please submit a case via https://support.planview.com.
Thank You,
Cloud Operations