Short description of your issue:

<amp-ad> tag with type "ping" is loading everything correctly, but the ad never shows: the iframe inside the <amp-ad> is being deleted.

How do we reproduce the issue?

https://bachtrack.com/amptest.html

Just load the file, and watch the Network tab on developer tools. You will see that the iframe is created, the source remotetest.html is loaded into it, that the console.log() statements in remotetest.html are all executed correctly, and that the ad image is fetched correctly by the browser.

If you set a breakpoint, you can verify that the iframe is there by looking in "Elements".

However, at the end of the run, the iframe has been deleted. The <amp-ad> tag is there, but the iframe is not.

What browsers are affected?

I'm on OS X El Capitan 10.11.6: the problem happens on all of Chrome (v 53.0.2785.143), Safari, Firefox.

Which AMP version is affected?

The AMP version is 1475106123549

This is a new problem - it was still all working on 28th September, and was broken yesterday (4th October).