- Your clients use IE
- Only have problem when using Intranet like URLs
- IE 11 Emulation (or IE10 document mode) is showing IE 7 or older or even quirk mode (however, if you see Edge then the solution I provide below won't help you)
- DOM view showing your nice HTML5 doc type being commented out
|IE commented out doctype|
IE option "Display intranet sites in Compatibility View" forced it to emulate behavior of older browser for Intranet web applications, regardless what is in the web page's header.
This worked for me: change IIS HTTP header