If you've been trying to install the April Update to Windows 10 and have hit a road block there may be a good reason. Microsoft has stopped the software from installing to computers running Avast Antivirus after some people experienced a blank desktop with no icons. This follows issues with installations on Intel and Toshiba SSDs which Microsoft has issued a patch for.
MartinZ, a product manager with Avast posted a message on the company's forums saying "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".
Whether that means the problem is specifically related to Avast, or Avast and some other, as yet, unidentified piece of software is still unknown. But another staffer from Avast is asking for affected users to send in system logs from the "C:\$WINDOWS.~BT\Sources\Panther\" folder to assist with the investigation.
This follows problems with upgrading to Build 1803 on systems running Intel and Toshiba SSDs. Tom's Hardware identified an issue that resulted in some systems with Intel SSDs to enter a UEFI screen reboot or crash repeatedly. That issue affects Intel SSD 600p Series or Intel SSD Pro 6000p Series, and Toshiba XG4 Series, Toshiba XG5 Series, or Toshiba BG3 Series SSDs.
Microsoft has issued a patch for that problem.
I don't envy Microsoft having to support such a massive variety of different system configurations. Issues like this, that seem to affect very specific configurations must make testing very challenging.