To make it faster for you to move around each newspaper page, we break each page into a number of small 'tiles'. When you zoom in or out, a new tile will be loaded that is specific to the part of the page you are looking at. This saves you downloading the entire page, which could be a slow process.
Depending on the speed of your internet connection, it could take a moment for the new tile to download fully and become clear. If you wait a few seconds (without moving around within the viewer) the new tile you are looking at will download fully and become clear to read.