Hi Guys,
Sorry for the late response.
So the issue turned out to be quite a strange one. Not sure if anyone has come across it in the past? Basically what happened is that the rule were authored on Exchange 2016 server. When looking at the same rule on an Exchange 2010 server it was visible but all of the logic/rules were missing. I deleted and re-created the rule on Exchange 2010 and the issue was resolved.
Basically the emails were coming in from ProofPoint to the Exchange 2010 server where the blank rule existed so it was not triggered.
Mike.