Windows 10 version 1803 was recently released to MSDN and other media. If you have Remote Server Administration Tools (RSAT) installed before upgrading from one release of Windows 10 to the next, then it’s worth noting that it (RSAT) will be automatically uninstalled. This is because it is a Feature on Demand and cannot be automatically upgraded by Windows setup.
So if you just upgraded to Windows 10 version 1803 and you used RSAT, then you can download the version compatible with Windows 10 version 1803 and install it. You can download it from here: