Frontpage changes to needs-rebuild after couple of minutes

I’ve recently changed to wp super cache to a project i’m working on and i figured out that something weird is happening on my frontpage. So far I haven’t seen it on any other pages.

When I visit the page the cached files are generated in the cache folder with the filenames: index-https.html and index-https.html.gz
But after a couple of minutes their name changes to index-https.html.gz.needs-rebuild and index-https.html.needs-rebuild until someone revisit the page in order to be generated again. If noone visits in the following minutes they disappear.

In the settings I have expirement a lot. My last settings on Cache Timeout is 0 in order to delete cache only manually.

Why is this happens? I want all the pages to be cached until I delete them manually.
The first byte takes 2-3s when it needs to be cached and less than 0.2s when it’s already cached.