Hello Everyone,
just sharing here what happened since the last post.
In the past days, Kevin gave me access to the system and we finally found that there's no issue in the (simple) way Moodle has been migrated to HTTPS: the issue is in the old Flash-based packages, being unable to properly work under HTTPS.
The package has been tested under a plain HTTP/S site w/o any LMS support: being that content able to selectively activate the tracking if running under an LMS. we found that under HTTPS it is unable to go further in loading the next layouts&content.
No further investigation done since the content gave no debug messages about what is going on when running under HTTPS: crossdomain.xml is not applicable here since the content is on the same domain of the host (i.e. it is served by the Moodle Files API, under the same "domain" settings)... neither the "standard" Adobe recommendations.
HTH,
Matteo