They sometimes go out of sync with each other. In my experience, this has happened in Super TIU mode (DCS version 4.2) when one engine enters another TIU zone when the command is sent to the pair and not picking up on it, or power interruption on one of the units. What I've found solves the problem is shutting down the consist, then selecting and starting each locomotive individually, then selecting and starting the consist.
This kind of thing also sometimes happens with a "sparky" derailment. The engines may mistake the pulses as a command. Usually re-starting the consist solves that.