Script Assertion works manually, fails executing Testcase

I have a script assertion added to an Assertion Teststep that is working when I run it manually but that fails when executing the Testcase.

The TestCase has:
- 21 Test Requests,
- a 45 minute Delay Teststep and
- 21 Assertion Teststeps using data retrieved from the 21 raw requests of the Test Requests executed earlier

My script assertion only has a call to a script I have in the script Library I created.

company.aProject.aSubProject.aFunction(log, context, messageExchange, anID, anotherID, '15');

When I execute the 21 Script Assertions inside the 21 Assertion Teststeps manually, they all pass.

When I execute the TestCase as a whole, all 21 Assertion Teststeps FAIL and the Message column in the Script Assertion Line of the Assertion Teststep states FAILED - null.

Any idea why it works manually but seems fail executed in the TestCase?

This is the content of the function I call:

def static company.aProject.aSubProject.aFunction(log, context, messageExchange, anID, anotherID, interval)
{
  def groovyUtils = new com.eviware.soapui.support.GroovyUtilsPro( context )
  def requestHolder = groovyUtils.getXmlHolder( messageExchange.requestContent );
  def ID = requestHolder.getNodeValue("//*[local-name()='anID']"); 
  def keystore = messageExchange.request.getSslKeystore();   
  
  log.info keystore;
  log.info ID ;

  ..
  Lots of code that is not relevant to this issue  
  ..

}