I have a Samsung Galaxy Note 10 + running One UI 3.0 and Samsung Galaxy Tab S7 + running One UI 3.1. I have been having an issue with these devices for a while now where even though I schedule do not disturb to turn on around 10pm and shut off around 8am the next day I will be woken up by notifications going off on my phone any time from 3am to 5am the next day. I reset all the settings on both devices and left my tablet on basically the factory settings. It seems to be working for my tablet but as soon as I adjusted the settings for do not disturb on my phone I started to have the exact same issue. I work in retail and so my schedule fluctuates. Some days I have to wake up at 5 am and some days I don't have to be up until 10 am. So I set 3 different do not disturb schedules all set for different days. I also can receive a call that I have to answer at any time of the night so I set that contact to favorite and do not disturb to only let phone calls through from favorite contacts. Then I started to have that issue again. I deleted all the schedules and just set it so I turn it on and it stays on until I shut it off. I will still be woken up by Twitter and Facebook at 3 am to 5 am. I read online that some people say that the digital wellbeing and wind down mode overrides do not disturb but even that doesn't makes sense. Wind down is set to turn on around 11pm and turn off at 7am. I don't see how that would cause do not disturb to turn off around 5am let alone 3am. Even when I did turn off the digital wellbeing wind down mode my phone did the exact same thing. My tablet has been running on the factory do not disturb settings and the same 11pm to 7am wind down schedule with no issues. I really think that its some kind of settings bug with do not disturb that really needs fixed. I'm coming to my witts end with this and getting close to factory resetting my phone. Constantly waking up and feeling tired or getting migraines because I can't sleep through the night is just awful! Any suggestions? I can't keep going like this.
Try using Bixby Routines to activate do not disturb when you want it to come without setting it on do not disturb itself. That may help. Leave it as not used but have Bixby Routines activate at set times.