Why does changing the 'UNIDADE' variant result in a negative discount percentage?

Store Design
1

When I change the “UNIDADE” variant, the discount percentage becomes negative.

Can someone help me? Thanks

site: https://www.ajetshop.com.br/products/babycare-1

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@Tamires2 - can you add me to the site? we will need to check the exact code which is showing these values