Slicer selection not working for line

Hi All,

I have 3 tables in my data model. Screenshot below.

Basically, this is a survey data where Q1 & Q2 were two questions. People from various sites participated in this survey. Data of the 3 tables below:

Q1:

Q2:

Site_Summary:

Now, the requirement is to create a Line and Clustered column chart for each question with 'Global' represented by a Line and the rest of the sites represented by Bars. Measure being the sum of Response_Count. I was able to achieve it using the below DAX.

DAX for Line: CALCULATE(SUM(Q1[Response_Count]),Q1[Site]="Global")

DAX for Bars: CALCULATE(SUM(Q1[Response_Count]),Q1[Site]<>"Global")

My chart for Q1 looks like below with 'Site' from 'Site_Summary' table under Column Series and 'Response' from Q1 table as Shared axis. So far so good.

The problem comes when I select 'Global' from the slicer. My chart goes BLANK.

However, it works fine when another site is selected along with 'Global'. Screenshot below.

What could be the reason? How do I solve this?

I have also given the link below to download the PBIX file.

https://drive.google.com/file/d/1Qf9n6DP4fgJ9BDSNhu5sfdTxRiXWtX9N/view?usp=sharing 

You help would be greatly appreciated.