I don't know what you're trying to achieve with this ([Int by Assigned ESS]='1') but we should find here your KPI without the condition ='1'. If you wish to apply an additional condition, it should be found in your set statement.
The formula should look like something like this :
=(SUM({<[InterviewCompletedDate.autoCalendar.Date]={">=$(=MonthStart (Today ()))<=$(=MonthEnd (Today ()))"},[Int by Assigned ESS]={'1'}>}YOURFIELDKPI))
I don't know what you're trying to achieve with this ([Int by Assigned ESS]='1') but we should find here your KPI without the condition ='1'. If you wish to apply an additional condition, it should be found in your set statement.
The formula should look like something like this :
=(SUM({<[InterviewCompletedDate.autoCalendar.Date]={">=$(=MonthStart (Today ()))<=$(=MonthEnd (Today ()))"},[Int by Assigned ESS]={'1'}>}YOURFIELDKPI))
