As stated above, re-fixing won't harm the film if that's the cause here.
I use tubes for developing 4x5 and 5x7, and occasionally will also see these marks (green or blue) after the fixing stage. I determined that it was due to the base side of the film touching the inside of the tube and not getting sufficiently "wet" during processing, resulting in residue from the anti-halation layer A few additional minutes in Hypo-clear solution in a tray and they always go away.
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