Windows 8.1.1, all the updates till now.
Same here, same problems, same way. Uninstalling Avast fixed all the issues brought by KB3000850. Issues (at least at my end) were, problems with:
Control Panel,
God Mode (some other win functions too),
No shutdown or restart,
Hybrid Shutdown works to some extent (Shuts Windows but not computer)
After Avast uninstall ( Avast own tool in safe mode), Windows Defender is not returned to previous state and WD service is completely missing. Dism /online repairs did not bring it back.
To top it all, no valid response from Avast team, explanation how windows update broke Avast is completely unsatisfactory, ignoring problem, even more so.
Not caring for their product or customers, put's any product on my black list despite many years of use, recommendations and installations on many computers, mine or customer's ( both free and commercial versions). I didn't notice any other major AVs to have those problems.
In conclusion, Avast has slipped badly lately. Not working on Win 10 TP (while many other AVs do), I can get over but braking a major OS is unforgivable. Ad to that affair with spying and it's enough for me to wish it a swift demise.
My recommendation on many IT forums I'm active on, will be BYPASS AVAST !!! GET RID OF IT if you use it. !!!