I think that can be a little Bug - here is my *.capx
Change the "Y" in the Parallax Settings in Layer 0 to Null an the Text with the FPS is no longer visible..
Maybe it is my Error?
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Closing as not a bug: layers with parallax 0, 0 display relative to the dotted line in the top-left of the layout. You need to move the object inside the dotted area for it to display.