AJAX Thumbnail Rebuild recreates the resized copies WordPress makes of every image in your media library. It does them one image at a time, so a library of any size gets through without running into the script timeout that stops the plugins which rebuild everything in a single request. You need this whenever the sizes change: a new theme with different dimensions, a plugin that registers a size of its own, or a size you have edited yourself. WordPress applies those to images uploaded afterwards and leaves everything already in the library at its old dimensions. Rebuilding fills the gap. On its...
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