Microsoft shipped Windows 10 October 2018 Update (version 1809) on October 2 but it was pulled shortly after its release. It turns out that there is another bug in the OS that resets brightness after a reboot on some systems but Microsoft has already figured out a fix.
After upgrading to Windows 10 October 2018 Update, some users are reporting that the brightness level is reduced after reach reboot and changing the brightness setting manually makes absolutely no difference as the level is automatically reduced after the computer restarts.
According to a thread on Reddit, there are some users experiencing this problem. Another thread indicates a similar problem on Windows 10 October 2018 Update. There is also a thread on Microsoft answers forum documenting the problem.
It appears that the brightness control is completely broken on Microsoft Surface Go for some users. According to a Reddit post, the October update has disabled the ability to adjust brightness manually on Microsoft Surface Go.
“Following the October update, I can no-longer control the screen brightness on my Go either through software or through the hardware keys on the keyboard. The hardware keys indicate that the brightness on the screen is going up and down, but it is having no effect on the luminosity of the screen,” a Reddit user explains.
I've been generally happy with Windows 10 feature updates, but this one has been a disaster on the Surface Go. Brightness is broken, battery drains in standby (no indication of why in "powercfg /sleepstudy"). Time to 🤞and attempt rollback, I think.
— Ivan Zlatev (@ivanzlatev) October 16, 2018
The fix is arriving soon
Microsoft yesterday released Windows 10 19H1 Build 18262 to Insiders with a fix for the brightness bug. It’s likely that Microsoft will now also fix the bug in Windows 10 October 2018 Update soon before the public rollout.
“We fixed an issue resulting in the brightness sometimes resetting to 50% after a reboot,” Microsoft explains in the release notes of Build 18262.