Hello
Something strange happened when I ran the sample (DataGridExtensionsSample) you provided.
Here are the steps I took.
Step 1 : Reset all filters on this page.

Step 2 : Uncheck the second and fourth items in the fifth column

Step 3 : Check the "i" and "p" in the ninth column

Step 4 : Uncheck "3" in the eighth column

After that, the previously filtered columns become unfiltered.
Thank you!