From my experience, the only time the left right volume balance does not work, is when the ‘wrong’ speakers are selected as default.
On the sound panel (> left click on speaker icon at bottom right, > sounds > playback), we usually see first “Speakers – FX sound audio” balance will not work with this selected. Then below that usually something like “Speakers – Realtek High Definition Audio,” left click and select this as default, and the balance control works once more, and FX processing remains active.