An exception will be raised if the value of the UpdateAction parameter is uaFail.
DoNotRaiseExcetionOnUaFail: boolean = False;
Starting with MyDAC 5.20.0.12, if the OnUpdateRecord event handler sets the UpdateAction parameter to uaFail, an exception is raised. The default value of UpdateAction is uaFail. So, the exception will be raised when the value of this parameter is left unchanged.
To restore the old behaviour, set DoNotRaiseExcetionOnUaFail to True.