With 0 as the second parameter, no date is returned. I have tested it out by having no restrictions on my [Date] field in the script and creating a KPI box with your expression in it. No date is returned.
I also tried inputting it straight into the script and it made all of my visualizations have errors. None of them displayed anything useful.
But perhaps I am misunderstanding. Please let me know if this is the case and you still stand by your answer.
Not sure but you can try today(1) to see if it makes the difference -
Returns the day of the last finished data load.
When used in a visualization expression, this returns the day of the function call.
When used in a data load script, this returns the day when the current data load started.
Returns the day when the app was opened.