Not able to change filter on Card visual

Hello,

I'm trying to update a filter on a Card visual however I'm not able to select the 'is less than' option. I created the following measure and applied it to a Line Chart, this worked correctly and the line chart visual does not display any information unless a Name has been selected from the name slicer.

However when I try apply the same to a Card visual I'm not able to amend the value. The drop down doesn't allow me to select and change it so that i can apply the same as above.

I'm fairly new to using pbi so not sure if it's something I'm doing wrong or if it just isn't supposed to work this way. 

Any help would be appreciated through!

Thanks,

Josh