QGIS Expressions: Can you filter an overlay function based on atlas variables?

Question

I'm creating an atlas of bus route maps in QGIS, and my goal is to show points of interest within a certain distance of a given route's line. I have 3 layers of note:

• routeLayer: LineStrings of routes. Contains a string attribute route that is also used as the title of each page of the atlas.
• bufferLayer: Hidden polygons surrounding each line in routeLayer, created with the Buffer tool. Also has route attribute.
• pointsOfInterest: Point layer. I want points to visible only if they're within the bufferLayer polygon that corresponds to the active route in the atlas.

In the symbology editor, I tried to use the following filter expression:

overlay_within('bufferLayer_[id]',filter:=route= @atlas_pagename )

Unfortunately, this always returned 0 features when I test the expression, so something was off. But here's where I got confused: If I set the atlas to an example route C51 and manually set the filter to

overlay_within('bufferLayer_[id]',filter:=route= 'C51' )

it works! What's more, in the Expression Builder, @atlas_pagename indicates it's returning the correct thing:

So what gives? Is there something about @atlas_pagename that prevents it from being evaluated inside an overlay function? If so, is there some other way to accomplish what I'm trying to do? Is there something else I'm missing?

Thanks!