Edits I made to my Layout will not update on the slides using it

I created a new, very basic slide master. Then I created a child layout with no elements on it whatsoever other than a gradated background. I successfully applied that layout to 28 slides. Then I added five custom buttons to the master slide.
But none of 28 slides are updating to show those 5 buttons. I have noticed this before where the slides in the scene do not update with changes to the Master.
How can this be?

 

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