Dates mess

Anonymous 

Sometimes you need to go from the most basic calculation to determine where the failure it. I would suggest building this in blocks. It is tempting to roll all of the logic into a single calculation but in situations where something breaks it is harder to find the issue. Plus, in measure, other than appearing in the field lists, you aren't really losing performance for having them available to build agains.

I would suggest first building a count and using it to create more defined logic.

CandidatesLast30 = CALCULATE(COUNT(Assignments[CandidateId]); PREVIOUSMONTH(Dates[Date].[Date]))

Candidates Added = COUNT(Assignments[CandidateID])   -- side note, in my data I would use DISTINCTCOUNT

Drop that calculation onto a table with the months as columns and see if it works. 

Does it work? Do you get the result you should? If yes, build a calculation for the previous month. I personally use DATEADD instead of the wrappers like PREVIOUSMONTH as I am old school.

Candidates Added Last 30 = CALCULATE([Candidates Added], DATEADD(Dates[Date], -30, Days))

Drop that on your table as well. Does it give you the last months total in the current month? 

Keep in mind that the filter for month needs to be set in the table or by the page for this to work. If you have just a card, you need to define current month in order for last month to attribute correctly.

If these measures work, you can build them into a single measure if you prefer using Var like this:

Candidates Added Last Month =

     Var CandidatesAdded = COUNT(Assignments[CandidateID])

     Return

     CALCULATE([CandidatesAdded], DATEADD(Dates[Date], -30, Days))