You have a lot of non-base-malt ingredients and dark malt in there. And your mash temp may contribute to slightly lower efficiency, too. I find that I always have to allow a few points lower when I do a stout or porter. When in doubt I formulate recipes so that it'll be to style over a pretty wide range of possible efficiency percentages. And I have a fair number of similar batches to reference to see where the average is likely to be for a particular recipe. We've all had things go the wrong way with efficiency or attenuation occasionally. All you can do is chalk it up to experience and brew again and see what the differences/similarities are.