Seedling with leaves struggling to open and slighly curved upwards

yeah, two plants can act drastically different. looks a little like ligh burn. if you've been watering properly and not fertilizing yet.. if the soil isn't too hot etc etc... lots of bases to cover. Usually too much light early on will cause the plant to fall over. could be heat-related, though. (photons or heat... 2 different forms of energy beating on the plant) I see you are fertilizing... stop. if that's in soild, stop twice. wait a long time before you feed... wait for a hint of deficiency in future few weeks, because you have put unused nutrients into soil where roots don't exist, yet. it has built up in that time... as new roots hit a new area, they get burned. conceptually speaking... seeds are packed with energy for a couple weeks... plus what you added plus the soil's contents (if coco only what you put in). Ease off the gas, and it'll recover. Even the healthier one has a burned tip.