These are just ERC errors since the nets attached to the MOS transistor do not have input ports so xschem flags these nets as unconnected. However these are driven by testbench voltage sources, so you can simulate with no problems. You can add '`noconn.sym`' components to these nets to switch off these ERC errors (meaning "stop giving these errors, I know what I am doing"). I will commit this change to switch off these messages.