When we try to change the post Author in the child site, we get the following issue, the author shows it has changed in the child post but when we view the post the original user “admin” from MainWP is still there.
Even when syncing the site in the dashboard it still shows the “admin” user.
The Authors don’t need to be created on MainWP for the Author column to properly reflect the author of a post.
This would indicate that this is not an issue with MainWP, but some other plugin is likely interfering with author change. Otherwise, if the author is properly changed, the front end would reflect it regardless of MainWP Dashboard.
One thing I’ve noticed is that in your screenshot of the WP Admin of the child site, the column is labeled “Authors” instead of “Author” which indicates that you have a plugin that handles post authors in some way.
A possible workaround would be to use a different, more fitting Administrator username to connect the child site to the MainWP Dashboard. That username would then become the “primary” author if you were to edit a post via the MainWP Dashboard, but it would prevent you from having multiple authors as set by the Co-authors plugin.