Windows 10 & Avast
Windows 10 has also been affected by this (1803 & 1809), during testing I've had issues on 3 W10 devices, which magically worked normally again once the update had been uninstalled in Safe mode.
This was caught on the W7 devices on the first test device and reported to Avast (via Barracuda who now own Managed Workplace) and so hasn't gone any further.
Avast have pushed out a micro update which needs to be installed and have a restart before the update then stops causing problems.
Sophos look to be working around with exclusions.
Fun all round....
I shall no doubt be moaned at for taking so long on updates this month!