At Dvina it was moved because of Vietnam experience I think. /edit: you wrote it already :-)

Why it was moved at Volkhov I do not know. Maybe lack of space, but there is some on the launch panel.

By the way, why PUSK and VOZVRAT button position was swapped at Dvina and Volkhov? Because the PUSK buttons are at better position for pushing than if they were at the lower row and you can accidentally flip the switched on the panel beneath them?