Visual Studio 2015 or 2017 shows IntelliSense errors but solution compiles

Similar problem as others, but different resolution. Posting in case I can help someone else.

Running Visual Studio 2017 15.5.2. I use Git and frequently switch branches. Several weeks ago, I started having editors show me errors (all related to types it could not find even though references were valid). Compile worked great. I confirmed the same issue in VS 2017 15.6 Preview (Jan 6, 2018). I would try to delete cache, SUO files, or bin/obj folders and no impact. At first it would appear to work. Reopen Visual Studio and everything would look good. Use "Rebuild Solution" and the IntelliSense errors would returns. I even tried uninstall/reinstall of Visual Studio.

I had the same issue on two machines, both with same version of Visual Studio.

By looking at the errors about missing types, they all appeared to come from two referenced projects. One of those references was a shared project used by just about every other project in the solution, but one of them was a small project without many references. It just so happens that the small project was also referenced by my larger shared project. In Visual Studio, I unloaded the small project and reloaded it. The errors went away! They errors did not come back on Rebuild Solution.

I then switched Git branches and the errors all came back. Fortunately I repeated the above steps of unloading/reloading the small project and the errors went away.

Every time I switch Git branches, the errors come back until I repeat that process. There are zero changes between the Git branches for the smaller project that I unload/reload. Unclear why that sequence is fixing my issue.

Ran into similar issue in Visual Studio 2017 ASP.Net Core Project. Following steps did the trick for me

1. Perform Clean Solution
2. Close VS
3. Delete .suo file & Delete bin/obj directories
4. Reopen VS

Also had this problem with a migrated project, so I referenced the Microsoft.CSharp dll. In some projects I needed to remove and add again the Reference in the project.

I had thousands of intellisense errors and 0 build errors. After deleting .suo file and restarting VS intellisense errors are gone.

Suo file is located relatively to source in: .vs\SolutionName\v14\.suo

According to comment: Beware that *.suo is a hidden file.

Edit: According to comments, VS2017 has the same issue, so you can use similar solution: Delete .vs\SolutionName\v15\.suo