Learning Alerts error for groovy expression on date format

We have several learning alerts setup from an Oracle document (https://support.oracle.com/support/?anchorId=&kmContentId=2786113&page=sptemplate&sptemplate=km-article) which have been working as expected.

But now when we go into edit the alerts we are getting the following error message about an invalid groovy expression on the date format. The only date we have in the alert uses the following expression - ${AlertUtils.formatDate(activityDate,\'dd-MMM-yyyy\')}

Can anyone help with why this is now now working, and what expression we should be using instead to get the activity date