I'm no expert but it looks like a bit of rot to me. Both on your sprouts and the bottom lower right edge of your leaf. If you are watering every two days.. it may be that the soil in the bottom of the pot isn't drying out, even though the top is. Can you stick a finger throught the drain hole and feel the soil there? If not, you can also use a wooden kabob skewer. Place down into the middle of the medium. When you check, you just pull it out and place on your cheek. Cool means you're good, dry and warm means time to water.
Not sure what your best course of action is if indeed you have rot.. maybe go ahead and cut the top leaf off and repot? Or maybe seperate your sprouts, cut the unhealthy portion off and transplant? I'm sure someone on here will know better
FWIW, I have a leaf cutting in a pot and have it inside a bag (to keep the humidity up). It's been there over a month, and I haven't had to water it once. The leaf is green and glossy and couldn't look better. Still waiting for babies though..