A key part of Koken involves image generation and caching. Koken creates images by using image processing software installed on your web server. This process takes your uploaded images and generates smaller versions for use inside Koken and on your public web site. A variety of image sizes are generated for optimum load times across all screen sizes (phones, tablets, desktops, etc). Once smaller versions of images have been cached, those cached versions are re-used for optimum speed and performance. A cached copy of an image is only generated again if you replace its original file with a new version.
Koken considers several factors when creating cached images, including the size the image will be displayed in your site theme and whether or not the end user is using a HiDPI (also known as “retina”) screen. In all, Koken has the potential to create 28 different caches for each image you add to your library. That’s a lot of images, and more than most shared web hosts can handle being requested all at once. To workaround that limitation, Koken creates most cached images on-demand as needed to avoid overloading your web server.
Also, try deleting the contents of the storage/cache/api folder via FTP and see if that helps.