I have the same issue with current version. In fact Avast is blocking many other Windows from staring normally, and it causes severe degradation of Internet performance (notably in sites accessed with IPv6, which fail to load successfully, but also suffer from a severe degradation of performance when they work, including with basic "ping -6" which was faster on all sites than "ping -4", but now IPv6 ping takes twice the time, with about 20 milliseconds added to IPv4.
Apparently Avast is using an internal very slow VPN or relying of IPv6 through IPv4, even if we have native IPv6 connectivity)
Internally Avast is also using an incorrect version of the WinRT runtime, trying to use the x86 (32-bit) versions in WinSxS instead of the amd64 (64-bit) version of components in winSxS: this causes lots of bugs in a native 64-bit installation for 64bit native applications that should not be proxied to the WinRT runtime used only by AppX applications built with the Universal Windows Platform (applications of the Windows Store).
I've run the AvCleaner in Safeboot mode, and Windows (fully updated) was fully functional after reboot.
Then I resintalled Avast, and I see again applications at startup no longer starting normally and many errors signaled in the Event Viewer about WinRT Runtime (cannot load xxx component, incorrect model, conflict between x86 and amd64 versions)
It seems that Avast is not compatible with a recent change in Windows 10 application "models", notably for how it resolves locale-dependant resources with some resources partially loaded from a neutral locale and others loaded from a fully localized version. This change was made by Microsoft to allow integrating several legacy configuration panel settings in the Windows 10 SystemSettings AppX (it uses now a Settings broker that allows interoperation/proxying between applications using different execution models): the Avast antivirus does not seem to correctly interpret the integration options that allow different execution models to run and be synchronized across distinct processes.
So Avast is no longer functional in Windows 10 (since build 16188, which was broken in various locales, and still now in build 16193 where it was fixed by changing again how execution models are integrated and how localisation resources are resolved and loaded from the Windows component store in WinSxS: I know that these are "insider" builds).
I had to uninstall Avast completely again (rebooting in safe mode to run AvCleaner and rebooting again) and the system was back to fully functional. To make sure that my system was not corrupted, I have run SFC /SCANNOW (in normal mode and in Safe boot mode), and DISM /ONLINE /CLEANUP-IMAGE /RESTOREHEALTH (does not work in Safeboot mode) and they detect no problem at all. The problem is clearly in Avast.