How to count days between two dates grouped by two attributes?

Hi D_PBI ,

If I understand your issue, please try this.
My example:

Period = 

Var _id = MAX('Status'[ID])
Var _series = MAX('Status'[Series])

var _MinDate = CALCULATE(min('Status'[Start Date]),FILTER(All('Status'),'Status'[ID]= _id && 'Status'[Series]=_series))
var _MaxEndDate = CALCULATE(MAX('Status'[End Date]),FILTER(All('Status'),'Status'[ID]= _id && 'Status'[Series]=_series))
var _dateDif= DATEDIFF(_MinDate,_MaxEndDate,DAY)

Return _dateDif

Let me know if you have any questions.

If this solves your issues, please mark it as the solution, so that others can find it easily. Kudos 👍are nice too.
Nathaniel