It is not a "myth/legend" but a well established fact. This caveat applies to ALL developers.
From the photo it appears to be something on the film and not an artifact caused by edge effects.
For the umpteenth time may I say that semi-stand and stand development were never intended as a general purpose developing technique. They are intended for tonal compression of contrasty subjects. Any book on the zone system will make this point perfectly clear.
That is why I suggested as 3.5 ml doesn't quite make the minimum as well as getting uneven development with semi or stand developing.