Disolved "feric/iron" salts, picked up and carried on the fuel/water, from tank to float bowls... Invisible as a solid during the formation, but once allowed to "sit" in the aluminum floatbowl, electrons bonding occurs, and they re-form into "larger" crystals, which you see after storage.. filtration is ineffective for removing the dissolved microscopic structure.. it's basically like dissolved into the solution.. and only 're-forms" when it sets in the bowls.. in the presence of oxygen., then sticks to the surfaces of the bowl, as fuel evaps.
Having had "cheapo" clear plastic filters, on various bikes, and never "seeing" any contaminants, but having the filter body break, and an inopportune time, dumping fuel, and requiring an "emergency splice on the road".. I choos not to ever have that happen again, and the metal "can" NAPA filters, just don't cut it for me, as I can't see the fuel in them either...
Just my personal observations, and if the bike is run regularly, and during storage, tank topped up, and stabilizer used, and no "half tank air with moisture" sitting.. it's about as good as you can do. No filter, that will flow fuel well, will prevent that "micro migration", as the iron is dissolved, in the liquids.