Hi,
I think the items are being rolled together by partnumber. The description can be *Varies* if multiple components have the same partnumber and are rolled. If the component have different descriptions, *Varies* is shown. There is one known issue with the BOM roll-up if Save Copy As is used and an instance of the copy is placed in the assembly. The BOM sees the old instance and the copy instance as having the same partnumber and rolls them mistakenly. I have an workaround for it is to save, close, and reopen the assembly. The BOM should be corrected.
Cheers!