I was getting a "dojo.js:24 Error: multipleDefine" and then I moved "<script defer src="https://js.arcgis.com/4.6/"></script>" to just before </body>. It got rid of the error, but my map still wasn't showing up. I was bringing in the map Javascript from a separate js file.
I wrote a custom Drupal module to handle it all.
Any help appreciated.