Well not ALL boas are alike..even if you house them together (which you might get some flack for that) it doesn't mean that they are both going to shed the same. Some require a bit more humidity than others. What i like to do when my boas are going into shed is mist their bodies daily until they shed, i feel it helps them, or atleast has helped mine. Hope your next shed is a good one!
Make sure ur temps and humidity levels are good