MissingReferenceException: The object of type 'ModularAvatarShapeChanger' has been destroyed but you are still trying to access it.
Your script should either check if it is null or you should not destroy the object.
nadena.dev.modular_avatar.core.editor.ShapeChangerPreview.IsChangerActive (nadena.dev.modular_avatar.core.ModularAvatarShapeChanger changer, nadena.dev.ndmf.rq.ComputeContext context) (at ./Packages/modular-avatar/Editor/ShapeChanger/ShapeChangerPreview.cs:70)
nadena.dev.modular_avatar.core.editor.ShapeChangerPreview.OnFrame (UnityEngine.Renderer original, UnityEngine.Renderer proxy) (at ./Packages/modular-avatar/Editor/ShapeChanger/ShapeChangerPreview.cs:174)
nadena.dev.ndmf.preview.ProxyPipeline.RunOnFrame (UnityEngine.Renderer original, UnityEngine.Renderer replacement) (at ./Packages/ndmf/Editor/PreviewSystem/Rendering/ProxyPipeline.cs:184)
nadena.dev.ndmf.preview.ProxyObjectController.UpdateRenderer () (at ./Packages/ndmf/Editor/PreviewSystem/Rendering/ProxyObjectController.cs:92)
nadena.dev.ndmf.preview.ProxyObjectController.OnPreCull () (at ./Packages/ndmf/Editor/PreviewSystem/Rendering/ProxyObjectController.cs:131)
nadena.dev.ndmf.preview.ProxySession.OnPreCull () (at ./Packages/ndmf/Editor/PreviewSystem/Rendering/ProxySession.cs:101)
nadena.dev.ndmf.preview.PreviewSession.GetReplacements () (at ./Packages/ndmf/Editor/PreviewSystem/PreviewSession.cs:51)
nadena.dev.ndmf.preview.ProxyManager.OnPreCull (UnityEngine.Camera cam) (at ./Packages/ndmf/Editor/PreviewSystem/ProxyManager.cs:42)
UnityEngine.Camera.FireOnPreCull (UnityEngine.Camera cam) (at <b41119cc6741409ea29f63c7f98de938>:0)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&)