Hi Mark,
Something went wrong with the settings so that why the particle didn’t work like it should.
You can give a try with the particle quickstart package, I just tested the particle quickstart with the same routing config and its working.

You can create a hidden menu item with Menu Item Type -> Category Blog and Choose a Category -> TMR News then assign your Base Article layout to this menu item.

Next, assign the menu item ‘TMR News’ with menu item type: Gantry 5 -> Custom Page

Let me know the result.