That worked like a charm. Thank you, it is much appreciated.

Not something I want to try on a production box then. So you're recommending that I try reinserting the missing Maintenance Plans folder row into sysssispackagefolders?

That's an option, but could be rough as quite a few jobs have been added/altered since the issue began. Is it possible to manually recreate the Maintenance Plans folder and...

I don't see any of the maintenance plans in msdb.dbo.sysssispackages, but I can see the subplans in msdb.dbo.sysmaintplan_subplans.

The output of the query against msdb shows only an agent job...