Your humidity was too high, more than likely. Were you using a hygrometer, or just winging it?
I use a little giant (styrofoam) incubator. Mine has the fan kit installed and I use an egg turner.My last hatch I switched to the dry method and highly recommend it.
W/o monitoring by a hygrometer or monitoring the air cells, chances are, as scflock said, the humidity was probably too high. If your humidity is too high, your eggs don't loose enough moisture and teh air cells do not grow big enough. This will cause them to drown when it is time to hatch. If your humidity isn't high enough the air cells will grow too big and the chick can become shrink wrapped by the membrane. Proper temp and humidity, are very important for a good hatch.
Dry incubation method is not adding any water to the incubator the first 17 days (as long as the humidity stays at or above 25%) and monitoring the air cells to check size for appropriet growth. There are many pictorials on line as well as one on the Hatching 101 page here on BYC: https://www.backyardchickens.com/a/hatching-eggs-101 The egg pic will show how large the air cell should be at key days of developement. Then day 18 when you go into lockdown you up the humidity to at least 65% or MORE, open your vents/plugs if they aren't already open and don't open the bator unless you really have to until they hatch.
The only way to know exactly what is going on in the incubator is to measure it with a hygrometer. I highly recommend doing that, but I'm going to be realistic and assume you might not. If you don't, and are flying blind, here is what I would do. Don't fill up all of the water channels at first. That's way too much humidity. Only fill one or 2 for the first 18 days. When you go into lockdown, fill up all of the channels. That is the best advice I can give if you aren't going to measure, but I highly recommend you get at least one thermometer and hygrometer.
