I use peat instead of vermiculite, I think the peat has some added antimicrobial aspects to it.
Also I make sure that I squeeze the peat almost free of all
water before adding it to the bags, you want it moist but not wet.
I like to check them every few days and mix up the baggie to allow for some air to enter the baggie, just by shifting around the peat and seeds a bit.
Like you said, mold can happen. Sometimes it has no effect, sometimes it takes over.
I had pecans pop open with tons of bright blue mold and had no effect on their healthy neighbors, I had Akebia mold out and take the whole baggie.
I wouldn't try the alcohol or peroxide straight up, maybe a very dilute solution, but mostly I'd wash them with water or leave them. It could be your seed just went bad or the mold may even be normal.
Good luck! What kind of seeds are they?