* Long click on clock icon -> Click in the "i" info button -> Advanced -> Battery -> Battery optimization -> Click on the "Not Optimized" button -> All Apps -> Scroll to Clock -> Click on Clock -> Select "Don't optimize" -> Done

Then go in the clock app, add a new alarm in 2 and 3  minutes
Reboot your phone -> wait for the first alarm (Nothing more, no unlock and no sim unlock) : first alarm should ring
Unlock the sim and unlock the phone : second should ring