This error in the Google Search Console is normal and depending on the Google management of cached URLs. Indeed Google needed to disallow direct crawling of cached URLs using a robots.txt file at the CDN domain: https://cdn.ampproject.org/robots.txt
More informations and policy about crawling Google AMP Cache URLs by bots can be found here: https://docs.google.com/document/d/1V_uLHoa48IlbFl7_3KWT_1JmCf6BnFtt3S_oR4UsasQ/edit
Google wants to serve cached URLs on its own without the need of direct indexing of those pages by crawlers that must index only actual URLs.
This misleading error message appeared recently in the Beta version of the Google Search Console and it will be probably fixed at a later stage by Google.
To avoid false positive error messages in the Google Search Console and to ensure a correct and quick indexing of new AMP pages, consider to switch off the AMP CDN cache parameter under plugin settings: