If you have set your Pricing Rules Setting 3 to be "Beat BuyBox by" this feature is designed to compete with the BuyBox until you take it. Once you have the BuyBox your price will remain the same and won't reprice as this could cause you to lose the BuyBox.
If a competitor takes the BuyBox from you then you will start to reprice against them until you take it back. If you want to compete with other sellers even if you have the BuyBox select Setting 3 option "Beat Competitors By".
NB. This only applies if you have your pricing rules Setting 3 to 'Beat BuyBox By'.
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