Can you confirm something for me; does the Invalid XML error occur on initial start-up only or on every time you either click the reload button or modify the filters?
That does sound like an issue fixed in the last release (v22.214.171.124) but in that case the projects never actually loaded.
Otherwise with the projects not loading, are they different in any way to the 21 projects that do load? For example are they master projects, or another special type? Master Projects are not supported by Bulk Edit, but all normal Enterprise or SharePoint task list projects should work.
Finally are the projects missing Published and visible in Project Center normally?
Thanks for the info.