When chicks drown during lockdown after internal pipping, it's not because your lockdown humidity is too high. It's because your humidity has been too high all the way through the incubation and your eggs haven't lost enough moisture. The chicks will still be alive at lockdown, because they aren't breathing air yet. When they pip internally into the air sac and start trying to breathe air, they inhale the excess fluid and drown. So even though they drown during lockdown, the cause of the drowning is not your lockdown conditions.
Solution is to lower your humidity right from day 1. If you're not sure how to get your humidity spot on and figure out if your eggs are losing enough moisture, consider weighing them. Chicken eggs need to lose approximately 13% of their starting weight by the time they reach lockdown. If you weigh them before you stsrt incubation, and then periodically throughout the incubation, you can track their weight loss progress and decide whether you need to adjust your humidity mid-incubation. It's actually really easy, and it instantly puts an end to all the usual guessing about humidity.
Yikes: Just read your blog and realised you've got another batch going into lockdown very soon. My advice obviously won't help them. If they've been over humidified, I'm not sure what you could do to increase their chances of survival now. I've read contrasting advice about hatching them on their sides or in egg cartons to reduce the risk of drowning once they've internally pipped, but I've never tried it so I'm not sure what is most likely to work. Chicks usually pip on the top of the egg, so away from any fluid, but then if the eggs get rolled around the chick could end up face down in the fluid and unable to breathe.
If I was you I think I might place them in egg cartons, but at a slanting angle depending on the line of the air sac. That way the chick hopefully has a chance of pipping internally and breathing air, cause all the fluid will be at the bottom of the slant. I think I might watch for the pips then once I see them, make another hole on the top of the egg and carefully try to drain off the excess fluid. That's just a wild idea though and I have NO clue as to how likely it would be to work...
