I would have been worried about helping too soon. A couple of mine had externally pipped at 4:30 am and didn't hatch until around midnight. Hatching takes them a lot of work. Assisting too soon can cause more harm than good. Lockdown is lockdown. I still think there was nothing you could have...
Some just aren't strong enough to thrive. Could have been anything, really. You had a pretty successful hatch rate. Don't think you could have done anything differently.