Select All from dropdown list does not work

Hello everyone,

I have created a page that contains an Azure map, a drop down list, and a table. The map displays the data of the table in bubbles, and the drop down list is used to select and show individually any of these data on the bubbles. I have also added the Select All option which does not seem to work as when I select it, the last chosen option is displayed as you caan see in the screenshot.

Do you know how can i resolve this?