The following table is not present in the WordPress database: wp_mainwp_stream

That is strainge,

Can you try to install this version on the child site:

and visit the following URL on the child site:
/wp-admin/options-general.php?page=mainwp-reports-settings&try_uninstall=yes

At the bottom of the settings page, you will find this option:

Please click the link and see if that helps.