A couple hours of direct sun should not cause withering. You may have a fungus gnat infestation. Do you see gnats flying around? They lay their eggs in the damp soil and the larvae feed on the roots. Check one withered one and see if it still has roots. Gnatrol will kill the larvae, but once the leaves wither, it's too late. The leaves wither because there are no roots. Do a search for fungus gnats. Not a fun lesson, but many of us have lost some pretty good cuttings due to those gnats.

Fungus gnats are puppies and kittens compared to their primary food source, fungus. Fungi can eat wood! No animal alive can do that, termites "eat" wood but they rely on microbes in their guts to digest the cellulose for them. Fungus gnat larvae can only eat delicate root hairs, fungi can eat a mature tree.

"Dirt" is not the right term to use, did you use soil? Potting mix? Compost? The shock from adjusting to water may have been the problem, tough to say really I have only tried water a few times and it did not go well for me. Soil is not meant for containers, it might work sometimes but never as well as a proper potting mix.

Did you unpot the wilted ones and look? The longer you wait the more chance you will miss what the real problem is.

Thank you for all for your quick responds to my concern, but unfortunately I did not check before I removed a few leaves away. Since I only transplanted them to the plastic pots using potting mix + perlite (not dirt) for less than 2 weeks, I do not think that it was due to fungus gnat infestation because the other cuttings are looking good and healthy. I really have no idea how this happened to my 4 cuttings.