What does the Scan button do?
Whenever a digital display (for example, DVI, HDMI, DisplayPort, or Mini DisplayPort) is attached to the computer system, an EDID (Extended Display Identification Data) handshake process occurs between the computer and the monitors. This process notifies the computer what the capabilities of the attached monitors are (for example, compatible resolutions and refresh rates), and then the appropriate settings are applied automatically. You may need to press and hold the Scan button for five seconds to begin the process.
The Scan button can resolve intermittent connectivity issues between the computer and the monitors. If you press and hold the Scan button, the MST hub is powered down. When the Scan button is released, the MST hub is powered back on, which forces the computer to initiate the handshake process and detect the monitors attached to the MST hub.