So adding to this: When I add that missing subassembly to the cost group, it rolls the top level part just like I’d expect. The difference in the standard cost was that subassembly’s cost. So again, I keep going back to the same issue. The Costing Workbench seems to randomly omit certain parts and it’s one thing if it doesn’t roll them at all.. but in this case it appears to roll them but missing some of the costs. Yikes! That’s a scary thought.
Here’s the link to my other open post. I am going to mark this as solved since it seems to be the same issue.