That happens because the Loser Feedstore keeps the product around waaay too long instead of shipping it back to whatever company made the product.
Rice bran is guaranteed "bug free" for a year. After the second 50# bag of buggy pelleted rice bran, I turned my local Co-op in to the company they were getting the rice bran from
If the rice bran is pelleted, you can put it in a kitchen colander that is the mesh kind. Put a piece of waxpaper on a flat surface and strain the bugs & powder out of the pellets, a few pounds at a time.
If you're dealing with rice bran in powder form, you could always risk needing a bailbondsman by throwing it in the feed store manager's face after you call the company that made it
It makes me wonder what other feeds a feed store will hang onto, past the expiration date, and risk the health of some trusting horse owner.
I now buy my rice bran from Tractor Supply in the next county because they stock pelleted rice bran and the TSC in my county refuses to stock anything but the powdered kind.