This is a bit of an odd one … I was working away on a Xamarin Forms project and suddenly started getting dozens of the red squigglies in the code editor. I could compile the project, but intellisense kept showing all of these errors.
I tried cleaning the solution, manually deleting all the bin and obj folders in all the projects, reloading projects, re-referencing projects. It didn’t matter, whatever I did still showed all kinds of errors, most of them being of the type “the type or namespance name could not be found”.
Finally I was able to track it down. The solution was to find the offending project in the solution (i.e. the one that contains the types that are throwing the errors) and remove it as a reference from the other projects. Then add the removed reference back in to each of the projects (Note you only have to do this for the projects that are showing the errors). After that, the intellisense is reset and all of the squigglies are gone!