"Non-Indexable-Pages" are pages on your domain, that can not be found in search engine result pages, due to the settings on your domain. There are multiple possible causes why this might be the case.
For example, this might result from the robots.txt definition saying wich directory is not allowed to be crawled by search engines.

Another common reason is the canonical tag to another page. The canonical tag defines the page which should be indexed. So either the canonical should point to its self or to a page with the content you want to be indexed. Here is some general Information about the canonical tag: RYTE Wiki Canonical Tag

The redirect enables webmasters to define another URL address where the content the user is looking can be found. This is used, when old URLs are not available anymore. The most common redirects are Status Codes 301 and 302 here is more about ist: RYTE Wiki Http Status Code.

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