Not sure if this might help...
In previous versions, the exact same issue happened if the Milky Way brightness was NOT ticked
i.e Sky & viewing options -> Sky -> Milky Way Brightness (not ticked, same white sky)
Therefore it was not possible in earlier versions to switch off the Milky Way AND have Spherical Distortion Mirror.
Phil
Not sure if this might help...
In previous versions, the exact same issue happened if the Milky Way brightness was NOT ticked
i.e
Sky & viewing options -> Sky -> Milky Way Brightness (not ticked, same white sky)
Therefore it was not possible in earlier versions to switch off the Milky Way AND have Spherical Distortion Mirror.
Phil