Sophos is not updating
Microsoft has yet to acknowledge the issue; no support article lists the problem as a known issue yet.
It is still recommended to create a system backup before you install any new update for Windows on your machines.
On this page, enter your my NMSU username in the Username box and your my NMSU password in the Password box, to confirm that you are an NMSU affiliate. Make sure your Hard Disk is selected and click Continue.
What we know so far The issue affects pre-Windows 10 operating systems only, at least that is what is been reported at the time.
In other words: Windows 7, Windows 8.1, Windows Server 2008 R2, Windows Server 2012, and Windows Server 2012 R2.
Some of these machines are completely unable to log in, and some log in after a very extended period of time.
Avast suggests that users roll back the update as well and has published instructions on how to do so on the linked support page.