@bird Welcome to Microsoft Q&A forum and thanks for reaching out here.
As per the Azure IP Range documentation, these IP ranges are updated weekly to the list. Which may be the reason you are noticing this behavior.
To overcome this issue, I would recommend going with Azure Private link for secured connection. For more information about secure connection, please refer to this documentation: Azure Private link for ADF - Secure communication between customer networks and Data Factory
Hope this info helps.
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