Hi,
version: 4.0.3
was disposing instances and got error:
Uncaught TypeError: Cannot read property '_internalAbstractMeshDataInfo' of undefined
at t._activate
at t.render
at t._renderForCamera
at t._processSubCameras
at t.render
checked code and looks like this._currentLOD is undefined at that time.
Will try to create playground version, but meanwhile wanted to clarify some stuff.
Is type for private _currentLOD: Mesh; inside InstancedMesh correct ?
As for me it should be private _currentLOD: Nullable<Mesh>;, as firstly its not initialised in constructor,
also all usages except _activate have check before usage anyway. 
Thank you