Can't group by Date in a joined report

Question

I have a joined reports that has 2 blocks comparing the same custom object with different filters. The grouping field is called Date and is of type date.

When I add a third block, with another custom object, I lose the grouping and can't add it again. The new custom object also has a Date field with the same name and type.

What am I doing wrong?

Thanks

Answer 1

You can't group across objects with different fields. While they are named the same, they reference different data points.