This afternoon, I installed MainWP Dashboard on a clean WP installation and MainWP Child on the rest of the WP sites.
The problem is that the Manage Plugins / Themes page is not listing all the websites. By default, when the page loads, it doesn’t show any sites. I then select all the sites in the right column and click Show Plugins / Themes. It then displays only the last site from the select.
I can’t figure out what could be wrong.