Still see this bug with with Unity 2020.3.31f1. For me it’s not restricted to duplicated states, and occurs with newly created Animator Controllers and states. The workaround setting m_ObjectHideFlags from 3 to 1 didn’t fix it. After this bug manifests, the Editor become sluggish. When you select an asset in the Project it takes 2-3 secs to display the Inspector properties, and shows a progress bar for Hold on… Inspector.InitOrRebuild.
Bug Report submitted. Appears it’s probably a duplicate of this. More info in this thread.