Thank you Brenden.
I don't believe redirecting WWW to non-WWW would solve the issue of Google blocking the domain. Some pages on https://mysite.com are showing the Google Red security page as well.
Google treats the WWW and non-WWW as two different sites, even though I use the domain property on Google Search Console which encompasses all aspects of the domain (www, http, https...)
As I read on various forums, this might be a false-flag scenario, interpreted wrong by Google.
I'm still amazed how Google is (mis)handling this kind of issues.
For more than a week, Google Search Console didn't change the security error message.
They just ignore my 4 audit requests submitted during the last 9 days.
The most frustrating thing is that you cannot contact anyone from Google (no email, no phones).
At this point I'm out of ideas, and migrating to KX13 is out of the question, at least in the near future, due to high amount of customizations we developed for the past years.
I'm still hoping for a miracle.