If you localize a set of elements e.g. right-click-localize entire body of a page, it may pick up image elements as well, and "clone" them into the localized version.
This means they no longer track the main image and if you update the main image the localized image won't match.
Localizing assets is a feature on enterprise plans, however the bug is that this image localization can happen even if you are on the Essentials plan, which does not support localized assets. That means that when you're in an an alternate locale in the designer, the settings pane gives you no image options to see, change, or remove the localized asset state.
You can tell it's localized by looking in the nav. You will see a globe next to any items that are "cloned" and localized.
However, you can fix this by right-clicking the image element in the nav, which will give you a "reset all image settings" option at the top of the menu. This unlinks that image from the localized version and it will track the main image again.