I mean, that in some unclear circumstances, the CPU speed on Surface Book 2 / Surface Pro 6 goes down to 0,4 GHz and it stays there. You can check it by pressing ctrl+alt+del and see the CPU performance table. In normal use, CPU speed should be around 3,0 GHz.
There are a lot of details on the Internet already about this issue.
https://www.reddit.com/r/Surface/comments/aj2go1/throttling_to_04_ghz_huge_issue