I chalked it up to the weirdness in the plant, Bong. I have several seedlings that have done that even though they get uniform care. It doesn't appear to hamper them in any way.
That said, I still check them with a magnifying lens just to make sure there are no lurkers causing the curls. I'd show you a pic but the one seedling I have that still had it was defoliated by over-exposure to a new (and surprisingly powerful) LED grow light I was testing.

Hopefully, someone else here who has had the same issue has figured it out.

Pagan

It is hard to say without seeing them or possibly knowing what form/hybrid

of adenium seedlings you have.

My Mini-Size plants have curled and some wavy leaves and this is typical

of this hybrid.

Could be just some oddity as Pagan mentions.

Rick

Thank you, Pagan and Rick.

I had earlier segregated the two community pots that has those odd ducks from the rest of my adenium obesum seedlings and sprayed with soapy water.

Today, (2 days later) noticed leaves starting to uncurl. I took one leaf and looked through magnifying glass: saw microscopic-sized somethings resembling dust, and one tiny white aphid. But the aphids that I have been constantly battling are the yellow oleander aphids that are clearly visible. Maybe this is a different kind of aphid, or else the oleander aphids have developed forms of defense by curling leaves and hiding? (Now I think I'm freaking myself out.)

Then again, as you indicated, the curling just might be the weirdness and oddity of the plant. And maybe the aphids found a cozy place to breed.

Will take pictures and repot to individual containers and monitor closely.

Thanks again.

An update to Leaves Curled Under.

This photo shows how the plants looked last
February. Four adeniums in community pot
growing together for 5 months. There was
a community also of different kinds of critters under those curled leaves.

On Mar. 2, I applied Bayer’s 3 in 1 and the curling leaves
stopped happening. Then Mar. 11, seedlings
were transplanted into their own individual pots—the roots were not cut. Beginning
Apr. 2, flower buds started appearing on three of the plants—first flower
opened Apr. 11 (The pics are shown on the post,Fertilize in Bloom?)

IMHO the combination of not messing with the roots, the
application of Bayer’s, and the rains brought by a typhoon all triggered the
plants to flower earlier than others in my collection. Forum members’ inputs on this matter are
welcome.

-bong

Good eye, Gareth. I missed that the first time I read this post. I also see another towards the top center of the photo just to the left of where the two large leaves intersect. Sneaky buggers!

Bong it sounds like you have already treated the plant and the leaves stopped curling. Always nice to know the root cause.

Tracy