Along with what Mike said

the cost in the BOM comes from the item screen, cost field.  That is just a reference number usually referring to the price paid last time you ordered it.  That is NOT item average cost used for accounting entries.  On the item screen for inventory type […]

Resolution for 'BOM comes issue: 'cost of goods sold for an inventory assembly item is accounted as $0.00 on profit and loss' available: Yes.

The BOM comes issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the BOM comes issue yourself by looking for a resolution described in the article. If it is a complex BOM comes issue or you are unable to solve the issue, you may contact us by clicking here or by using other BOM comes support options.

For more information about resolving issues related to BOM comes in Quickbooks/QBO or to get support for the issue 'cost of goods sold for an inventory assembly item is accounted as $0.00 on profit and loss', click the link below: