This is the correct (and in my opinion only logical) answer. Despite CX online checkin flagging it, absolutely no issues checking in. As it should be.

Sometimes they manually write the middle name on the boarding pass when they know immigration are annoying about the match, but "middle name" is not an official field for many people or airlines. The match should properly be done on last/first.

Chinese or "three-barrel" names are different because it's a two word first name, not really a middle name.