There are missing components

Message

There are missing components on "<GAME_OBJECT_NAME>".

Explanation

Sometimes developers forget to remove a component they added to a game object for testing purposes and remove a script or a plugin providing this component. This might also happen during an upgrade when a newer (or older) version of Unity fails to find a component assigned to a specific object. This is going to manifest itself in Unity editor like the below:

Many projects (especially those with significant development history) suffer from this issue. While it might go unnoticed for a while, there are instances where such "ghost" components actually become an issue.

Steps to fix

Developers should either remove those components or re-assign them again with proper references.