My s10+ is playing my incoming call ringtone anytime the phone is turned off, restarts or sits on the charger overnight and hasn't been unlocked. If the alarm comes on after the above and I snooze the alarm without unlocking, it will play the incoming call ringtone again. If i unlock after a snooze it will play the correct alarm tone. If i set an alarm for a few minutes from now and don't turn off or restart, it will play the alarm tone. It seems that it wants to complete the "system is starting" message before working correctly.
I've cleared the app cache, system cache, uninstalled the app updates, reset notification settings and reset system settings. Nothing has worked. Samsung tech was no help. Both call ringtone and alarm ringtone are stock Samsung ringtones.
Let's try a soft reset on the phone. This will end all processes and give the phone a fresh start. To do this, press and hold the 'Power' and 'Volume Down' buttons until the phone restarts.
Let us know how you get on.