Google AMP test doesn’t find pages after activating HTTPS

Hi to all,

We activated HTTPS on our website: https://www.lanostratv.it.

AMP pages seem to be ok, for example:
https://www.lanostratv.it/2018/10/verissimo-a-rischio-silvia-toffanin-e-pier-silvio-berlusconi-bloccati-a-portofino/amp/

This URL pass the test on the AMP Project validator:
https://validator.ampproject.org/#url=https%3A%2F%2Fwww.lanostratv.it%2F2018%2F10%2Fverissimo-a-rischio-silvia-toffanin-e-pier-silvio-berlusconi-bloccati-a-portofino%2Famp%2F

But it DOES NOT pass on the Google AMP Tester:
https://search.google.com/test/amp?id=GW4QZml6o5gxWhbtix58sw

The message is (translated from Italian): “The page could not be reached – The reason could be that the page is not available or is blocked by the robots.txt file” (see screenshot: https://snag.gy/FtspJL.jpg)

Our robots.txt doesn’t block Googlebot, so where is the problem?

Thanks for every suggestions,

Marco