Thanks, Matt. My agitation, once each minute, was five inversions. I'm not gentle, but I'm not really shaking it up hard, either. Just go from one hand to the other, with a small twist each time, so that by the time I've done five inversions, the tank has been rotated fully, if not more. This is how I've always done it, in my limited time doing this. I have only used Rodinal, and I've only developed twenty or so rolls, with more than half using a stand protocol, unlike this time. But that's the agitation I use for the developing.....I've been much less rigorous about fixing

So based on the replies here, I'm definitely going to be more careful about fixing, both making sure the fixing time is double the clearing time, and also paying more attention to thorough agitation!

In this case, my first serious issue with development, the fix was potentially more dated and more used than in other cases, but it's still the first time this has happened, which leads me to ask the question:

Is there a difference between the steel reels and the plastic ones with regard to "access" of the film to chemicals, and need for agitation? In other words, even though this may have been caused primarily by old fix, is it possible I would have seen no problem, or less of a problem, had I used the plastic reel?