Your case is similar to
WS.verifyElementText keyword does not work when the response SOAP message has a <soap:Header> element in front of a <soap:Body> element. I checked it is the case in v8.1.0. This fact is not documented.
Your case is similar to
WS.verifyElementText keyword does not work when the response SOAP message has a <soap:Header> element in front of a <soap:Body> element. I checked it is the case in v8.1.0. This fact is not documented.