i bet its where the plant sprouted first then from watering your soil has settled and basically the old root is now your stem. thats what mine looked like... i wouldn't worry.. or if oyu are add some more soil
EDIT after looking back at the pics i believe thats what it is 95% sure.
lol, sry i was high when i did this i meant 1.2 weeks old (my bad). and its the only one really out of the other 6 ive noticed doing this and its kind of like wide u shaped chunks taken out of th sides. nothin big tho