A mysterious CPU throttling issue seems to be affecting select Surface devices such as the Surface Pro 6 and Surface Book 2. A report from TechRepublic explains today that affected users see their CPU being throttled to 400MHz, and you may have a higher chance of encountering this problem if you have installed recent firmware updates.
Many users have been complaining about this throttling issue on Reddit, and it appears that the cause could be Intel’s BD PROCHOT (bi-directional processor hot) feature that can automatically throttle CPUs to decrease the overall temperature of a device. Intel's BD PROCHOT feature isn't exclusive to Surface devices, and it's actually useful to prevent PCs from suffering damage due to overheating. However, users who disabled BD PROCHOT using a third-party utility called ThrottleStop have been able to solve the problem, as explained by Reddit user schmak01:
It's the BDPROCHOT sensor. Install throttlestop. You'll notice as soon as it goes to 400 mhz that the BDPROCHOT will go nuts. I think MSFT put in a bios update that makes the sensor too, sensitive. It triggers throttling way too early. This was probably done because of people complaining about battery. You can use throttlestop to disable it from throttling your processor. I have mine set that way for about a year now with no issues.
Microsoft confirmed the CPU throttling issue on Surface Book devices in a statement to TechRepublic. "We are aware of some customers reporting a scenario with their Surface Books where CPU speeds are slowed," the Microsoft spokesperson said. "We are quickly working to address via a firmware update," he added, without giving a specific ETA.