You cannot use an MST hub to increase the maximum number of displays that a video card supports. For example, if your video card only supports up to three displays, your display limit will still be three displays even if you use an MST hub.
If you have multiple MST hubs connected to the same computer and are experiencing display issues, you should check your video card to make sure that it can support the number of displays that you are using in your setup.
If you use an MST hub in your setup, your video card also needs to be compatible with MST technology. For more information, refer to the following FAQ: https://www.startech.com/faq/mst-hubs-gpu-compatibility.