Project file is incomplete. Expected imports are missing

You can check global.json file which you can find in solution root directory and make sure that the target SDK version in it installed on your machine or update it to one you already have it installed for example if you have SDK version 2.1.4 installed your global.json should look like this

{
  "sdk":
  {
    "version": "2.1.400"
  }
}   

Resolved

1. Even after uninstalling certain version from control panel, there would the files and folders with deleted version found in C:\Program Files\dotnet\sdk

2. Please go and delete unwanted version folder

3. Try reloading the project

This worked for me

Another potential cause is you installed a .NET Core version which is incompatible with Visual Studio. This might be unrelated to the original question by the OP, since it concerns different version numbers, but since I landed on this page while looking for help I thought this might be useful to others.

At the time of writing, I installed .NET Core 2.2.203 which is not compatible with Visual Studio 2017 (Professional 15.9.11).

The .NET Core download page lists a separate download for Visual Studio 2017. Be sure to download this one when you intend to use Visual Studio 2017. The current supported version is .NET Core 2.2.106.

I had the same issue. In my case, deleting global.json and appsettings solved the problem.