As promised I’m updating this topic so others having the same problem know what to do.
This is an issue related to the WordPress Network configuration, which have been set as sub-directories instead of sub-domains. This causes network websites to be accessed through example.com/subsite instead of subsite.example.com as expected by the OP.
However, if there is an individual WordPress installation which happens to share the same name as one of the network sub sites, it leads to think one is working with a sub site instead of a totally different site, so if we on top of that add a forced redirection from example.com/subsite to subsite.example.com, we will be accessing a website out of the network instead of the internal site.
As a result, it may appear that Network Latest Posts or any other plugin is not properly working. Network sites contain different information from individual sites but if an individual site shares the name of one network sub site, one may think they are the same which are not, and network plugins will seem like they are broken.
The solution for this topic is to install a WordPress Network sub-domains ready, delete any individual WordPress installations, reset any forced redirection, and configure each sub-site with their respective sub-domain. For further information about Network Installations please check the Codex article: Create A Network.
Best regards,
José SAYAGO.