We don't see indications of a pest or disease, and this appears to be abiotic (not caused by a living organism like a pest or pathogen). It's hard to see clearly what the residue is, but it might be exudates, which is secretions from the leaf, which can happen when plants are over-watered. A similar phenomenon is cystoliths, which are mineral (calcium, for instance) secretions by foliage that can be normal for some species in certain environmental conditions. The current conditions in the photos don't look too wet, but it's hard to say for certain. Make sure the potting mix isn't staying soggy and can dry slightly between waterings (and that is drains well). Using a fan on a gentle, low speed to circulate air over the sprouts may also help them manage leaf moisture and can reduce the risk of a fungal outbreak going forward.

Miri