Since version 4.4.1 MainWP Dashboard will display changelogs and plugin information for Premium plugins.

However, some premium plugins do not use WordPress standards to retrieve and display the changelog and plugin information on Child Sites.

In the case of such plugins, the information will not be visible on MainWP Dashboard.

If the changelog is required, please reach out to the plugin author and ask for the Changelog location so you can inspect it before running updates.

For Developers

Premium plugins need to use the pre_site_transient_update_plugins (for themes pre_site_transient_update_themes) filter to hook the Changelog and Plugin info, in order for WordPress to get that info.
Later, when MainWP Child uses the get_plugin_updates() function, it gets that info and synchronizes it to the Dashboard.

Please refer to WordPress Developer resources for more information about get_plugin_updates() and pre_site_transient_{$transient} functions:

get_plugin_updates()

pre_site_transient_{$transient}