I had this problem and found a fix for myself, but I'll let you know that it might not work for you. (Sorry if it doesn't!)
So, with mine, I realised that the Do Not Disturb function turned itself on when I was launching full screen applications (stuff like full screen games, stuff like Zoom, etc). And that, once I was out of these full screen applications, the Do Not Disturb mode still acted as if it were on.
I later found a setting in the security application "Avast" that there's settings to do with the Do Not Disturb mode.
So to fix it, I went to the Avast application, Settings menu. Under that menu, there's a tab for "Performance". And, in that menu, a setting saying "Silence notifications from 3rd-party apps", description: "Block all alerts while running your chosen apps fullscreen." I unchecked this box.
So now notifications appear for me while full screen applications are running, and it does not launch the Do Not Disturb function for me. In that portion, there's also a setting where you can choose which applications to allow notifications from or ignore while in fullscreen (click the "Don't block notifications from these apps" link to see that setting).
So, by doing this, I've avoided the problem occurring for myself, by simply not letting the Do Not Disturb be turned on by the application. But the essential problem (in my understanding) is that the software still thinks the Do Not Disturb mode is active, even when it's not; which is something that Microsoft developers will need to fix. (That sounds rude of me, sorry!)
It might work for some of you. Sorry if it doesn't work for you personally. Good luck! I hope the developers can get this problem fixed completely one day!
Edited to add: While mine was relevant to Avast, which you might not have, there may be similar software that you are using that has relevant settings to the Do Not Disturb function. So, maybe have a look at settings to do with fullscreen applications, and similar. :)