Did you perform Inventory Items → Recalculate action after the Purchase Invoice was entered?
If there is a positive number next to Inventory Unit Costs on the Inventory Cost Correction screen, it means the purchased inventory hadn’t been updated against the COGS table yet. This is why you don’t see COGS reflect on reports.
Always run Inventory Items → Recalculate after every inventory purchase if you need the latest COGS.
Also, keep in mind Manager.io uses moving average for COGS.