Time Intelligence

You are probably closer than you realize, so I will just throw this out there. 

Thinking about the dates as numbers it might help... 

If you have a value of '1 January 2017' in the DimDate table, it is represented as the number 42736. But if you have a value of '1 January 2017, 13:46' in the CloseDate field, it is represented as 42736.57 (you can check this in Excel by entering these values, then formatting the cell as a number).

If you have a relationship between these two fields, Power BI thinks that the values above do not match. That makes sense to a computer, because they are different numbers. That's why one column is blank while the other isn't when you add them to a table. But you want Power BI to assume that everything that happened on 1 January 2017 should be linked (regardless of the time it happened on that day). 

So you can try this:

1. click on edit queries

2. expand and click on the CloseDate column

3. click the Add column tab

4. Click the Date button and select 'Date Only'

This will add a new column that contains only dates (no times). Use that new date-only field in your measures, etc. and see if that helps.