Unity Issue Tracker - Entities Hierarchy window allows Cyclic nesting and throws an “ArgumentException: Cyclic nesting detected” error when dragging a Prefab onto the same Prefab in the Entities Hierarchy

Active

Under Consideration for 6000.6.X

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Issue ID

Regression

Entities Hierarchy window allows Cyclic nesting and throws an “ArgumentException: Cyclic nesting detected” error when dragging a Prefab onto the same Prefab in the Entities Hierarchy

-

Mar 31, 2026

Steps to reproduce:

Create a new Unity project using the Universal 3D template
Install the Entities package (com.unity.entities)
Click and drag the "Global Volume" GameObject into the Project window to create a Prefab
Open the Entities Hierarchy window (Window > Entities > Hierarchy)
Dock the Entities Hierarchy window somewhere visible
Click the right-arrow button in the Entities Hierarchy window to the right of the "Global Volume" to open in context
Click and drag the "Global Volume" Prefab from the Project window into the Entities Hierarchy window
Save (File > Save / command+s)
Observe the Console window

Actual results: "ArgumentException: Cyclic nesting detected" error is thrown

Expected results: Cyclic nesting should not be possible, Hierarchy V1 & V2 windows show a popup notificating the user when step 7 happens

Reproducible with versions: 6000.0.72f1, 6000.3.12f1, 6000.4.1f1, 6000.5.0b2, 6000.6.0a2

Can’t test with versions: 2023.1.0a3 (due to no Entities package)

Tested on (OS): MacOS Silicon Tahoe 26.3