Fyi, I copied the program update into the client's v2018.2 test system. Upon testing, I see that the ""Invalid bill"" messages are now gone. What I also noticed is that the items listed for a given BOM have changed. Before the program update, it appeared to just list the top-level (parent) items. But with the program update it's instead showing the components for the applicable sub-assemblies, and the top-level (parent) items that have no components.
I'm checking with Sage to find out if the 'items listed' change was also part of this program update. And btw, it appears the initial issue may be specific to BOM Options. Also, attached shows the report settings we're using.