We had tickets in our hand only to learn the night before that the excursion was canceled. By asking, not by being told. We got apologies (every time the director saw us from then on), a refund, and credit.
There are so many moving parts on a cruise, I'm surprised when things work without a hitch. Because I assume things will go wrong, I book once, check twice (at least). As long as Viking continues to buy us off with credit, I'm fine if they sometimes want to cover errors with a little mendacity.