https://dontkillmyapp.com/samsung
The “Put unused apps to sleep” option is the major headache we see on Samsung - a non-standard app-killing feature that isn’t present in AOSP implemented only by Samsung which puts an app you did not use for X days to a mode with restricted background processing. On some releases, the period was short as 3 days. So if you did not use your alarm clock over the weekend your alarm would not ring.
