The MainWP Child Reports plugin is installed on the client website.
However, the report shows 0 plugin updates and 0 theme updates over the past 30 days, even though I am 99% sure that there have have been plugin updates during that time frame.
MainWP Child plugin has had to be installed for the activity to be logged and it cannot show any activity retroactively.
Can you go to the WP Admin of the child site in question, then Settings > MainWP Child > Child Reports page, and check if there are any logs during the relevant time period?
Do you know if those updates were performed by uploading a ZIP file? If so, WordPress technically counts those kinds of updates as Installations/Activations.
Only updates performed through the Updates page will be logged as updates.