Since the filters are on the page, not the sidebar navigation, try moving them above the content that they are filtering. This way users won't have to guess why filters in the sidebar are turning on and off, or disappearing altogether.
Currently it looks like those filters might affect the navigation items below them, not necessarily the content.
It also forces me to look left back to the navigation once I've selected a page to go to. If I don't, I might miss some filtering choices.
One method is to put only the relevant filters into the content pane, and give more visual separation between the navigation area and the content pane.
Option 1. filters below the page title.
I moved up the title since it seemed there was a lot of space not being used:
Option 2. filters at the top
Either way the idea is to group together the information being potentially filtered.
Remove the irrelevant controls, rather than disable.
Test these with users to make sure that
- they see the filters
- they understand what the relevance is for the page they are on
Since they are separate pages, you could remove the unnecessary dropdown for pages that it is irrelevant to, rather than disabling.
Don't make the users guess why controls are turning on and off, and treat each page as a separate view space.