Google’s John Mueller said on Twitter that if you cannot have a clean header in your source code where Google can fully interpret the hreflang, then you are out of luck. Google said either fix the issue with your header or you really cannot depend on Google properly understanding your hreflang markup.

The issue came up with Akamai iframe broke the header and resulted in Google having issues processing the hreflnag. This was from Barry Adams:

John Mueller from Google chimed in to say they make no exceptions here, fix the issue or you are out of luck:

Forum discussion at Twitter.