The VT2600 is only capable of outputting a signal to 3 displays at any given time. In order to achieve all 3 external displays and your laptop screen the host system must support USB-C DP Alt Mode DP1.4, MST and DSC. If your system does not support DSC make sure to disable your laptop screen before enabling the 3rd display. If you are unable to disable the laptop screen, make sure to set one of your external monitors as the default display.