Disqualification can be related either to prolonged offline (more than 30 days) or to lost or corrupted data.
To receive emails about being offline you need to provide a valid email address in the node’s configuration, but it’s better to configure some external monitoring: How do I check my node when I'm away from my machine? - Storj Docs
Uptime on the dashboard is showed since the last restart, but it doesn’t mean that your node was online, it shows that this time it was running.
If your node was offline, its online score will be affected: How is the online score calculated? - Storj Docs
You may check when your node was offline: