“Remove unnecessary usings” not working in Visual Studio 2015

Question

I have a solution with a few projects. Remove unnecessary usings is working in all projects except for one.

Why does the Remove unnecessary using

Answer 1

Needing to set the Warning Level to 4 for code analyzers to fire is a Roslyn known issue.

Additionally, check your projects' Code Analysis rules (project properties > Code Analysis > Open). We had CS8019 and IDE0005 disabled, which prevents the code fix from being offered and the unused using(s) from being highlighted, respectively.