What began as a complaint on Reddit about botched upgrades to Windows 10 April 2018 Update, version 1803, has apparently mushroomed.
Now, according to MartinZ, a moderator on Avast support forum:Microsoft temporarily disabled the updates on version 1803 on PCs with Avast.
We are working together with MS to find out the cause of this issue, but unfortunately right now neither MS nor us are able to reproduce the issue.