“su: must be run from a terminal” with lxc

Question

I am trying to understand the following error and the solution

I connect to the lxc container with the following command

#lxc exec cont-01 -- sudo --login --user ubuntu

and after login in on the terminal when i execute a command to switch users

#su -l bob

I get the following error:

su: must be run from a terminal

The following provides a solution “Must be connected to a terminal error” with screen -x command on a Linux Container which is to execute the following:

#script /dev/null

I was wondering if someone could explain what the issue is and why executing that command solves the problem.