Hiii,, in your cell phone
1 . Go to settings
2. Then google
3. In google click on , "Personnel
4. Click there,, Turn off ,
Silence notification while...
This is the solution
This appears to be related to Bixby routines [this allows you to automate your phone to do things by your location, time of day, or activities] Galaxy phones appear to have default routines that are automatically enabled.
To fix your issue, swipe up on your Galaxy phone. then search for Bixby, you should get about 3results. Bixby, Bixby routines, and Bixby vision.
Select Bixby routines and delete any routines you have not created. If your issue was related to a routine that was activating "Do not disturb", This will surely fix your issue.
This was exactly the issue. Thank you! It was getting so annoying. For some reason, there was a Bixby routine set up to automatically detect when I was sleeping and would turn on do not disturb. I don't recall ever setting that up.