I've build an AMP version of (a section of) a website. The AMP pages themselves are tested and valid, and they have canonical links to the desktop site. That's all fine.
On the desktop site, I've specified the <link rel="amphtml"...> to point at the corresponding AMP page. All should be working, but in Google Search Console, I'm seeing an error: "Referenced AMP URL is not an AMP"
Now, the linked AMP pages are definitely valid AMP, so I'm getting cranky.
The only thing I can conceive being a problem is the desktop site also has a <link rel="alternate" media="only screen and (max-width: 640px)" href="[mobile version of site]">... perhaps Googlebot is confusing the alternate page with the AMP page?
To be transparent, I don't have much access to the desktop site - I can't actually remove the <link rel="alternate"> code.
Thoughts? Insight?
Further Info:
In Google Search Console, the linked AMP pages is being reported as "not an AMP":
However, if you run the URL through the AMP validator, it passes as expected: