If you've opted for Confect to remove backgrounds, the images are cached and must be reprocessed.
Images don't update automatically because many websites regularly change the image link without changing the image itself (i.e., through URL params "image.jpg?date-stamp"). The images are cached in order to prevent the product from being sent to background removal again and again, making it unavailable.
If only a few products need to have their image updated, find them in "Products" and press "Reprocess image".
If too many products have changed their image, contact us in the live chat so we can mass-process your images.