Perhaps there are grounds for appeal. In the Chamberlain case (2nd) the court said that the proper approach for evaluating circumstantial evidence was to apply the standard of proof to each purported fact, and if each fact did not pass muster it was to be discarded from consideration. Only then, after all purported facts have been thus individually evaluated, should an attempt be made to evaluate guilt, using only those remaining facts which have not been discarded.
That doesn't seem to have been the approach of CAS, who seemed to take a fuzzier (I'm being generous here), more holistic approach. This is the type of issue that a Swiss appeals court would be able to consider. Another avenue would be CAS' approach to "no significant fault", allowing us to appeal the penalty if not the finding.
Non-lawyer here, so I have no idea whether such an approach to circumstantial evidence is also mandated for Swiss law, whether Australian law is of any relevance at all, whether we can appeal to Australian courts, etc. etc.
Of course, a cabal of lawyers will be considering all such angles for Essendon right now.