Male flowers?

The problem here is it looks to be a full pollen sac, rather than a lone nanners. Lone nanners often produce inviable pollen or none at all. An entire pollen sac has the full compliment of male anatomy to produce pollen. It's more concerning. Since it's already fallen off, the stress that caused it was 4+ weeks ago, if not just genetics-caused. Not finding others is a really good sign. If they aren't all over the place, i'd definitely keep it. This particular pollen sac already released whatever it was going to release and your circulation distributed it. Damage is done already. Check nearest areas where you found it for rusty pistils (pistil death occurs at pollination, so you'll see premature coloration of pistils, if so). Hopefully it's still early enough that it can be distinguished as far as assessing degree of the problem. Anecdote - i'm pretty lazy about this stuff nowadays. I see a sac or two when harvesting occassionally. Never have a problem with seeds... I may find a few from a 32-35sq ft canopy worth of buds. Plants that hermie without much stress is a bad trait to pass on. The seeds will all be XX (female), that is gauranteed, but potentially more inclined to hermie, too. Gorilla glue was an accident like that. I still wouldn't bother with any seed from a plant that hermied on its own - selfed or not.