Defender Portal - Sensor Health State is wrong

Hello,
We use the Vulnerability Management module in the Defender Portal and our IT is completely in the cloud.
Now I have the following situation, which I cannot explain. Some hosts have the “Sensor Health State = Active” although this server no longer exists.

I have read in the documentation that the Sensor Health State is set to “inactive” after seven days.

So I don't understand why the server is marked as active.

The "Last Seen"-Timestamp is also older than two months. 

Can someone explain this? 

What exactly does the Health State Sensor mean? 

Thanks and Kind Regards, 

Tobi