One of the common issues we see with blank or zero values in payment reports or invoices is that a commission rate is not being set for the vendor. The commission rate can be set under the "payment setup" in the dropship provider settings.
If commission rates are not used and instead cost / wholesale pricing is, then the cost prices might be missing for the brand. It's possible to export a list of the missing cost prices from the menu in the top right. This will only show if the commission rates checkbox is turned off.
Changing the above settings (or most of the invoicing options) likely won't impact any current invoices. For example, if you switched the commission rate or another setting and the invoices still appear as zero or blank, you'll need to go back and reset the prices on the purchase order. This can be one from the main purchases menu. Or, within the payment report itself.