First off, I haven't migrated away from the Toolbox. Doing so would eliminate the need for this issue. That is best persistent way forward. This problem I am having only applies to Toolbox components, which may or may not be relevant. Descriptions do not come through from Toolbox components when populated in a BOM.
When I create a BOM in a drawing, I can interact with each component which is lacking a description by Opening the part, and it identifies what size or material options apply because it opens that component with the selected configuration active. Then I note applicable variables, and manually overwrite the description field in the BOM with the appropriate text.
Today, I tried creating a BOM in the Assembly, which I've never done before. It was difficult to work with. Selected cells to edit would display the text very large, usually spanning width greater than my window, cutting off the beginning and end of it. Zooming out the view did not help this. More relevant to my question, when I opened components which lack description, it opens that part in the last saved configuration, and not the referenced configuration of that BOM line item. So, I have several blank line items which are all configurations of Heavy Hex Nut, but I cannot manually distinguish which size is represented for each.
I GAVE UP on trying to use the assembly BOM, and made a drawing to add a BOM to where it is much easier to distinguish these configurations as described above. My task is completed and I have moved on. However, is the difference in behavior of Open component - either representing the applicable configuration or not - an intentional behavior, or an error? Is there a Setting to make them behave the same? I think I am just going to avoid assembly BOMs as fairly useless and unnecessarily difficult to manage and edit.
Ref. install 2018 SP2