Assertions Pass in Test Case but Fail in Load Test

Hello. I am trying to create a Load Test from a Test Case, and the assertion that I used successfully in the test case fails in the Load Test. My test case is fairly straight forward. Step 1 is Data Source retrieval from XML. Step 2 makes the Soap call. Step 3 runs the assertions. Step 4 is the data source loop. When running in load test, the error is Xpath Match Failed. Not sure why it is successful in test case but fails in load.

This is the assertion I am using:

Declare
declare namespace com="http://oss.companyname.com/xsd/service/Common/CommonServiceMsg";
//res

Expected Result
<res IsSuccess="true" xmlns:com="http://oss.companyname.com/xsd/service/Common/CommonServiceMsg" xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <exception>
    <errorCode xsi:nil="true"/>
    <errorDescription xsi:nil="true"/>
    <errorType xsi:nil="true"/>
    <errorShortDescription xsi:nil="true"/>
    <errorBusinessDescription xsi:nil="true"/>
    <errorStack xsi:nil="true"/>
  </exception>
</res>