The pattern is one I've made before Simplicity 3678, the Threads collection knit dress. I'm not sure what the deal is with the threads dresses. I've made two of their coats and one of their skirts and they seemed true to size, but the two dresses I've made have been ginormous! I would normally cut a 12 with an FBA (sometimes) at the top and a 14 in the waist and hips, but in the threads dresses I can cut a straight 10! I found this particular style was big in the back too (my back is a little narrow). Here is my previous effort.
I can look back with humour now and I consider it a lesson learned about being aware of my own limits but at the time, let's just say I didn't have quite such an 'adult' perspective on it. I suppose it's one quick way of reducing my stash!