it's more confusing because it moves between the 1st and second frame, although is the same shape- and on the last one it is the same as on no 2, but there is a second leak going right across the film.
I couldnt begin to work out where it is coming from ... the usual rule is opposite upside down for the source, but as this seems to start some way into the frame rather than coming from the edge, it makes it a bitmore difficult. did you process these yourself or did you get them done at a lab? might be worth looking at a leak in your changing bag or dev tank too???
PErhaps it's worth getting in touch with the Arax man again and asking if it's a common leak/ fault.