Impossible to turn back after changing visualization from "flat" to "jerarchical" on Performance page

Hi,
as title says, I’m struggeling from strange behavour that seems to be a little bug.

During data analisys in “Performance” page I changed visualization from “flat” to “jerarchical” one.
But when I tryed to turn back to on “flat” again, the “cog” button disappear and now I’m blocked on “jerarchical” visualization.

I’m doing something wrong, or it’s a bug?

Thanks in advace!
Bye