Thanks for your detailed and helpful response, Peter!
I went through all of your links and I found several matches between the examples provided there and our situation, especially for what concerns the domain's recency.
We'll have a couple of weeks of patience to see if something in Google's SERPs is moving, otherwise we'll start trying to "force" search engines to start seeing and trust our site. And also maybe ask directly to Google for a re-evaluation.
Many thanks, I'll update this post if something relevant will come up, in order to help other facing similar issue that can occur them in the future.