This issue could be related to the theme’s code or possibly a conflict with any customizations or apps you have installed. To troubleshoot this, I recommend checking the code in the product page template (product-template.liquid) and ensuring that the quantity update is properly linked to the subtotal calculation. You can also try temporarily switching to a different theme to see if the issue persists, which can help identify if it’s specific to the Elle theme.
Same you can check for the cart page also.
If you’re unfamiliar with Liquid or feel uncomfortable modifying the code yourself, I recommend reaching out to Shopify support.
Remember to create a backup of your theme before making any changes and test thoroughly to ensure the desired functionality is restored.
I hope this helps resolve the issues you’re facing. Good luck, and please feel free to ask if you have any further questions!