Are editorial cutbacks the cause?:
15 across: Argentine plainsman fully backing emperor (7)
Both Wikipedia and the Spanish Royal Academy confirm it: a llanero is from Colombia or Venezuela, not Argentina.
10 across: Cruise line largely ill-advised to strike malign… container (8, 3)
A pandora’s box is 7’1, 3 in length, and not 8, 3.
28 across: Engrossed in computer, private nerd makes Sudoku (5, 6)
I was considering granting this to DA on metaphorical grounds, but then I thought against it: a magic square is something that a Sudoku puzzle most definitely is not.