There may be a device setting affecting this… Here are a couple of possibilities:
https://forums.androidcentral.com/google-nexus-7-tablet-2012/234476-disable-sleep-mode.html
There is also a strong possibility that depending on the version of Android that Samsung is using and their localizations, or changes my by your phone carrier, they may have created a situation where the normal way to manage this via software no longer works.
The Corona default is to allow the screen to dim and eventually go into sleep mode unless you explicitly turn it off.
Rob