Presumably, this is 35mm film since SFX200 has only recently become
available in 120 roll film.
If the stripe is at the edge it may be residual anti-halation dye.
If so it will be on the back of the film, not the emulsion side. In
general anti-halation dyes are not removed during processing but are
converted to a colorless form. They can revert to the colored form with
time or under the influence of certain chemicals. It is not unusual for
some residue of anti-halation dye or even unfixed halide to remain at
the edge of the film since the reel of many processing tanks prevents
access of the processing solutions there. If that is what happened here
there is probably no reason to worry about further damage. You can
check for the anti-halation dye by treating a small bit of the film in
a print developer like Dektol. That will decolorize any residual dye.
So should a sulfite wash aid. If the developer treatment works you can
soak the whole film in it for a couple of minutes to decolorize or
remove the dye and wash it for about five minutes to remove the
developer.
--
Richard Knoppow
Los Angeles, CA,  USA
dickburk@ix.netcom.com