There is a change in the latest version of the Chrome browser, v51, which has had an adverse impact on ArcGIS Online, Portal for ArcGIS and some apps built on JS API v3.8 – 3.16. ArcGIS Online and Portal for ArcGIS are currently unusable on Chrome v51. Esri are working directly with Google and are in the process of creating patches for affected products.
We advise customers to use an alternative browser until this problem has been resolved. There will be further announcements regarding this in due course.