The FMG16 New Window CARD option to 'Dim Parent Window' doesn't always work. If you close a window (which is a card) then open a new window (which is another card) a few steps later, the 'Dim Window' option doesn't seem to have enough time to take effect.
A work around is to use a Pause step after you close the first window card. A Pause of 0.25 seconds is the lowest time that gets the 'Dim Window' to work again.
iPhone 7 Plus iOS 10.3.2