Not hitting the Workflow

Hi,
 I am working on a module, where i need to upload payments massively and after that i need to approve those payments. As i  am using Windows Workflow service for this purpose of approval.
Following problem i am facing during submission of Payments massively.
> When i am trying to uplaod payments massively(near about 500) few payments are not hitting the workflow. For ex, out of 500 payments 50 random payemtns are not hitting the workflow. i came to know this after seeing that few payments didnt pick the Rule, even though the rule condition satisfy.
> when i am trying to approve few payments even though i can see that those approvers details are saved in ApproverTracking table, but approval is not happening. Might be loosing the instance but not sure.
So for the first problem, what could be the issue and how can i track those payments which didnt hit the workflow as it is async call and it is happening randomly.
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