The red circles mean there was an error while scanning those devices and the thread was killed. It could be a consequence of either:
- The user clicked the Force button in the Stop Scanning dialog. This is not recommended, as it forcibly terminates the thread and results in a memory leak. Devices with terminated threads are marked with the red circle.
- The user set a run-time limit in the settings, which lets threads run no longer than the set time period. For example, if the maximum run-time is set to 60s, after a thread has been running for 60s the application will attempt to finish it gracefully. Failing that, in double the time (120s) the thread is killed, likewise causing a memory leak and marking the device with a read circle.
In other words, a red circle indicates the thread was killed due to either of the above reasons.