As of today's date you can only run one locomotive at a time with the LionChief App. Where as the Universal Remote allows you to run 3 locomotives at a time.
In the screenshot below it shows 2 available LionChief Plus engines, but you can only run one at a time with the App. The other locomotive has to run with a Universal Remote or a second LionChief App installed on a different device.
If you try to run both of the Available Engines at the same time, they will both stop running and go into the beeping mode.
Hope this helps. Gary