Why some line items have a $0 value:
There could be various reasons why certain line items show a $0 value. Enabling negative inventory might explain some instances, where available inventory contributes to the value on sales orders, work orders, or similar transactions. For instance, if there is no inventory available, you won't be able to add the item to a transaction properly, resulting in no value being shown.
Other causes can be a bit elusive, but they can often be identified through a ledger-style report. This type of report outlines numerous data points, helping track down issues related to standard costs and more for each item in the system.