Grand total doesn't work when I apply drop down filter

Hi all.

I’m trying to do page grouping for my website, to analyse which page is work better.

So I put new field on the data resource of my looker studio GA, as my report is a direct data from my website GA. Is a simple formula that I use as its shown below

But now come the issue, as I put a drop down filter on my report to navigate the page, my grand total doesn’t work when I choose only one data aggregation as show below

However when I didn’t choose (show all data) or choose the page that not grouping the grand total works perfectly.

Can anyone help?
Thank you!