WP blog in subdomain and Google indexing

Of course the blogs Urls (https://mydomain.com/myblog and https://myblog.mydomain.com) are just an example to illustrate the architecture of the mine, I apologize to anyone who is owner of the domains above listed.

Use example.com when making example links. example.com is reserved exclusively for that purpose.

It might be helpful to us if we could see the actual blogs, to try to pinpoint any subtle differences.

Skippy, the real Urls of the blogs I described above are : https://primeitaly.com/italianclubs/ (here any post is indexed ok in Google)
https://pmi.exportfocus.com/ (here the posts disappear as ‘slip’ on the third page)