Hello,
From what I can see, the percentage sale label only works when a regular price and a sale price are both set on the product itself. If your discount is applied through promotions, then the theme’s built-in percentage calculation will not detect it — it only calculates based on the regular/sale prices.
If you are using a dynamic pricing plugin, you can disable the default “Sale” label under Theme Settings -> Shop -> Product Labels and instead display a custom badge or message using your plugin.
Best Regards,