The one shown last night is new, though IMDB says it’s the 3rd in the series. DH and I were puzzling over this, as we generally don’t miss a Beck (though it’s not been the same since they killed off Gunvald).
On further investigation, BBC4 showed the two previous episodes last year, both featuring the annoying grandson being his usual tiresome self. They’re just playing fast and loose with the scheduling, I think.
(The books are very good - nothing like the later TV series, which rapidly took on a life if its own!)