Hidden Viewport is not hiding background objects

This is very irritating. When working in Hidden Viewport, everything in the background is visible as you can see below.

This happened after disabling VisualARQ due to some hanging issues with the plugin. The plugin’s viewports (Hidden and Conceptual) are modified in order to show things better.
But now, after disabling it, I’ve started a new project with default Millimeters template and the viewports are showing everything in the background - solids, meshes, lines…
The 3D stuff are blocks created from surfaces.

I’ve tried modifying the viewport, even resetting to defaults, but nothing seems to work.
Can anyone help? I’m sure it’s something very minor and I can’t find it.

*These are the current viewport settings

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