I don’t think it’s a seed problem, storage at another place for 2 months is of no consequence. What’s your light wattage and spacing distance?
It looks too dry - coco is not the same as soil, it’s totally inert - there are zero nutrients for a seedling in coco so you must bottle feed weak nutes to her. Right now the only food those seedlings have are the 2 cotyledon leaves and those are merely backup energy for a day or two. Coco is drain to waste hydro so hydro rules apply, ph matters adjust from between 5.8 to 6.2, coco should not be allowed to totally dry out. Indirect air movement - fans moving air nearby help strengthen stems. Helmet heads can be softened with spray mist and then removed with a toothpick.
I‘m not a coco grower either but most feed quarter strength nutes so maybe go 1/8 strength for a seedling. Don’t be lazy & don’t guess but do the math to figure it out your dosage. Mix very small but fresh batches of nutes don’t let them sit around for days because nutes can bloom and grow bad bacteria, use syringe for accurate measurement.
20 mil per 128 ounces gallon
10 mil per 64 ounces half gallon
5 mil per 32 ounces quart......... in this example all are the same strength just smaller batches
thats all I’ve got bro, hope something sticks!