What's the issue?

amp-form via xhr not submitting at least in Edge 14.

How do we reproduce the issue?

Problem noticed on a private website, nevertheless it also exists on other amp-form powered websites, most prominently in the examples provided by the Project itself:
https://ampbyexample.com/components/amp-form/#form-submission-with-client-side-rendering

What browsers are affected?

At least Edge 14, IE11.
Latest Chrome, Firefox, Opera and Safari seems not affected

Which AMP version is affected?

Version 1902151859190
Not quite sure, never realized it before, I'm guessing it's a new issue.