Hmm, that’s weird. Are you using any widget visibility plugins like “Display Widgets”, “Widget Context” or Jetpack’s Widget Visibility? Without one of those plugins, widget should display throughout your entire website if they’re in the same widget area.
Just to let you know that the offending plugin in Yoasts WordPress SEO. I have to to disable and re-enable this piugin after making changes in the customizer or with widgets etc. It’s not the end of the world but it may help out knowing this in case it comes up again.