Why is this an issue?

There’s no need to null test in conjunction with an TypeOf ... Is test. Nothing is not an instance of anything, so a null check is redundant.

Noncompliant code example

If (x IsNot Nothing And TypeOf x Is MyClass)
    ' ...
End If

If (x Is Nothing Or TypeOf x IsNot MyClass)
    ' ...
End If

Compliant solution

If (TypeOf x Is MyClass)
    ' ...
End If

If (TypeOf x IsNot MyClass)
    ' ...
End If