This error happens on a new installation if you try to install the base-openrc package group. I've tested it on my main machine and a (as plain as possible) virtual machine. This doesn't interfere with installation but once you boot the system you will be unable to create any new users since the user group does not exist: "useradd: group 'users' does not exist".

I've attached an image with the exact error. Not sure what package in the "base-openrc" group triggers this.