I have seen a discrepancy, where the Hours were posted , but the actual cost is not populated.
When this is checked in the Posted transaction review , the amount is shown and it has rate.
I have checked with Query and I found other scenario.
From 2016 to 2018 there are 30 hours shown in the Posted transaction review for Project, Resource Task and it shows 4227 as the Transaction amount
For the same Proj,Res and Task .The Hours is 30 , but the Actual cost is shown as 1742.