Measure with Disconnected Table as Filter

The Syntax for values is we need to use either table name Or column name. 

VALUES ( TableNameOrColumnName) 

In your DAX you must use the column as 

VALUES(LeaveSummary

[GNA_ORG_NAME])

Please use the below function and try. 

LeaveSummaryDaysDynamic = 

    SUMX(

        FILTER(

            VALUES(LeaveSummary

[GNA_ORG_NAME]),

                 [Leave Summary Days] >= MIN(DaysGroup[MinValue]) 

                 && [Leave Summary Days] < MAX(DaysGroup[MaxValue])

        ),

        [Leave Summary Days]

    )

Please mark it as solved If it works. 

Hello - when a table is used in the VALUES function a table with the same columns is returned.  When a column is used in the VALUES function a single column table is returned.  LeaveDaysDynamic is calculating the leave days for each unique value from the [DET_NUMBER] of the EMLAC table with the min/max specified whereas LeaveSummaryDaysDynamic is being fed a table with multiple columns as it's basis.  Is the DET_NUMBER field also available on the summary table?  If so, you can use it inside VALUES. 

Documentation

https://docs.microsoft.com/en-us/dax/values-function-dax 

Return value

When the input parameter is a column name, a single column table. When the input parameter is a table name, a table of the same columns is returned.

Remarks

When you use the VALUES function in a context that has been filtered, the unique values returned by VALUES are affected by the filter. For example, if you filter by Region, and return a list of the values for City, the list will include only those cities in the regions permitted by the filter. To return all of the cities, regardless of existing filters, you must use the ALL function to remove filters from the table. The second example demonstrates use of ALL with VALUES.

This function is not supported for use in DirectQuery mode when used in calculated columns or row-level security (RLS) rules.

For best practices when using VALUES, see Use SELECTEDVALUE instead of VALUES.

KNP try this measure, let me know if it works, I guess you want to iterate over each unique row based on GNA_ORG_NAME & LAV_LVE_TYPE  to get the Total Days:

Leave Summary sample data you provided is not good enough to produce the issue because each row in the sample data is unique.

LeaveSummaryDaysDynamic = 

    SUMX ( 
        SUMMARIZE ( 
            LeaveSummary,LeaveSummary[GNA_ORG_NAME],LeaveSummary[LAC_LVE_TYPE], "@LeaveSummaryDays", [Leave Summary Days] 
        ),
        IF ( 
            [@LeaveSummaryDays] >= MIN ( DaysGroup[MinValue] ) && 
            [@LeaveSummaryDays] < MAX ( DaysGroup[MaxValue] ), 
            [@LeaveSummaryDays] 
        )
    ) 

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KNP if you see the diagram below, based on your sample data, In the red box, a new measure I provided, yellow highlighted your original measure, and Card visual showing total summary days and total matches everywhere. Something else is going on with your real model since you mentioned there are a lot more columns in the table, if you trim down your table to just 3 columns that you gave in the example and then test the measure, what do you get?

it is hard to debug what is going on with partial information

I've attempted to reproduce your issue given the data you've provided but I'm struggling a bit.

Can you modify the file I created or create your own version that you can share?

Thanks for the replies.

I finally got to the bottom of it. Source data that was supposed to be unique in the source system was not. Story of my life. 

Once I cleansed that, my original, as well as all the suggested measures also worked. I should have gone back to the source from the start.

Apologies for wasting your time.

Since I have your attention.

Assuming every row in the table is unique, is there a "best" or most performant way to write those measures?

e.g. SUMX(FILTER(VALUES(Table[Column])... or SUMX(FILTER(VALUES(Table), ... or SUMX(SUMMARIZE... another pattern?