Duplicate of BUG-000099447: This is a known issue that affects the following browsers:
Firefox 49 (Release Date: September 20, 2016)
Chrome 54 (Expected Release Date: October 18, 2016)
Safari 10 (Release Date: September 20, 2016)
Esri is working on a patch. Please review the following details:
https://blogs.esri.com/esri/supportcenter/2016/09/20/announcement-errors-encountered-in-arcgis-for-server-and-portal-for-arcgis-web-apps-after-certain-browser-updates/