There have been many different issues caused by the latest 1803 update to Windows 10 from Microsoft. The latest I have come across is the XPS viewer dissapearing.
Luckily the fix for this is a quick one-liner command from an elevated (Run as adminsitrator) Command Prompt:
dism /Online /Add-Capability /CapabilityName:XPS.Viewer~~~~0.0.1.0
If you get error after running this command, it is likely that WSUS is enabled on your machine and not working so should be temporarily switched off to allow the feature to install.
Open up regedit.exe from the Start menu and paste the following into the bar at the top:
Update UseWUServer to 0
Restart the Windows Update service:
net stop wuauserv net start wuauserv
Run the dism command once more.
Once The XPS viewer has been installed, don’t forget to re-enable your WSUS server and restart the Windows Update service again using the same stop / start commands above.