Hello....
Check another thing.
YOu are broadcasting a workbook. That means, you are using a Precalculation Server.
This Precalculation is installed on a Windows server.
Log on there (Windows) with the user that you are using on Precalculation Service (you may have to check firsrt - SERVICES.MSC).
Access Control Panel > Region and Language.
There, the date must be exactly as you required.
Then, save it and test again.
Should works.
Keep me informed if works or not.
Best Regards,
Edward