Once your tenant is using UPS (unified presence service), you should no longer have issues where DND changes back to available.
If you are on UPS, and are experiencing this issue, it would be super helpful if you can capture logs by typing Ctrl + Shift + Alt + 1, and send the file from your downloads folder along with any details to firstname.lastname@example.org.
84 votesAlfred commented
This is infuriating. Can this please be brought to feature parity with Skype?