Assets can be set to non-active manually or by the database cleanup options found under Configuration\Server Options. I would recommend checking your cleanup configuration. Keep in mind that, once an asset is set to non-active, it will not be set to active again unless you:
- Enable the following cleanup option and rescan the asset: "Automatically make non-active assets active when they are rescanned".
- Manually set the asset to active, e.g. by hitting the Edit Asset button on the asset page.