ScriptableRenderPipeline/com.unity.render-pipelines.high-definition/HDRP/Editor/Lighting/Reflection/HDReflectionProbeEditor.ProbeUtility.cs

namespace UnityEditor.Experimental.Rendering.HDPipeline
{
    partial class HDReflectionProbeEditor
    {
        void InitializeTargetProbe()
        {
            // For an unknown reason, newly created probes sometype have the type "Quad" (value = 1)
            // This type of probe is not supported by Unity since 5.4
            // But we need to force it here so it does not bake into a 2D texture but a Cubemap
            serializedObject.Update();
            serializedObject.FindProperty("m_Type").intValue = 0;
            serializedObject.ApplyModifiedProperties();
        }
    }
}