Steps to repro:

1) Create a new VFX graph, open it

2) Add Output Mesh Block

3) Assign some new SG to its Shader property, perform Undo

Error is thrown to the console. This error is also mentioned in UUM - 10400. 

{{Material 'Shader Graphs/VFX_Lit' with Shader 'Shader Graphs/VFX_Lit' doesn't have a color property '_BaseColor'}}
{{{}UnityEditor.EditorApplication:Internal_CallGlobalEventHandler (){}}}{{{}Material 'Shader Graphs/VFX_Lit' with Shader 'Shader Graphs/VFX_Lit' doesn't have a texture property '_MainTex'{}}}
{{UnityEditor.EditorApplication:Internal_CallGlobalEventHandler ()}}

{{Couldn't reproduce on 2021.3.11f1}}