Hi Nicaboye,
External monitor issues with the Surface Book can be caused by several factors. We suggest that you ensure your Surface Book has the latest updates installed. Also, check the firmware version installed on your monitor. You can go to your monitor manufacturer’s website to learn how to find your monitor’s firmware version, and make sure it's up to date.
Furthermore, some DisplayPort video issues can be resolved by disabling “MST mode” or “DP1.2 mode” on your monitor. Please refer to the owner’s manual that came with your monitor to learn how. If your monitor supports DisplayPort, we recommend that you use a Mini DisplayPort-to-DisplayPort cable, see if it helps.
Give us an update, and let us know if you have any additional concerns.
Regards.