What I’ve observed is they sometimes get stuck on their backs and then drown from the excessive amount of water they are drinking getting into their airway. After 2 had died I decided to do something about the slippery ground under the shavings which is what I am guessing is causing them to not be able to get back to their feet after they stumble on their back. Right now they are in a black tub from Cosco which is lined with cabinet liner now. On top of the cabinet liner there are shavings. I am using a quail chick waterer because the chicks are smaller Japanese bantams. I will attach a picture of the rest of the brooder setup.
Some people (including me) like to use a layer of paper towels for the first day or first few days. That provides good footing for the chicks, and also keeps them from eating shavings while they learn what food is.
I've read of other people using puppy pee pads for the same purpose.
You might be right about the slippery bottom of the tub being an issue. I'm glad you were able to fix it with the cabinet liner!