What could be the reason for this?

Too low rh might be calmag aswell

Probably temp/rh (VPD). You need low vpd and very low levels of light, initially. You slow transpiration down considerably. Without roots, the plant can't do too much too fast without hurting the cause. A little paling is not the end of the world, but adjust light to avoid paling in future as you tweak your method. i'm not one for buying useless shit, but you really should have some sort of domed setup to maintain a high RH / low VPD environment for cuttings. I would also get a heat mat with thermostat. Even in a dry climate, a heat mat and dome will trap evaporation from the moist media. 1020 trays are cheap and fit the 10x20 heat mats. get some 2.5-3" inserts or starter pots / plugs / rockwool cubes whatever floats your boat... Smaller pot is probably a good idea. you take some substantial cuttings, but jsut enough to hold it upright is fine... the more air penetration the better and you get that automatically from a smaller volume around the buried stem. Unlike normal irrigation cycles, you keep it moist top to bottom. if you got a proper amount of perlite or similar, ensuring saturation is fine and maintains proper drying pattering. Roots physically turn toward greater moisture as they grow. you want the bottom wetter than the top in a consistent manner and just spritzing the top does the opposite. None of this is make or break. You can toss a cutting in a jar of water and forget about it for two weeks and there's a chance it grows roots, lol, and a bunch of algea and whatnot but somehow survives. low vpd, low light... When you start noticing hints of vege growth or see a root, you can start to give more light, and start to expose it to a more normal temp/rh combo of your tent. if speed is of utmost importance, get an aerocloner or diy one. I prefer just wetting a medium and using a humidity dome with a slight delay by comparison but also avoid cleaing one more goddamn piece of equipment, lol.

The 2d cause coud be too intense light (same mechanism)

Cuttings? If u mean clones, then u,d cover em with transplant bag or cup, that will keep RH, otherwise they just dry, like u see on the pic (it defense mechanism... the leaf lowering evaporation surface by curling) Also keep 15-20k lux (not more)