I'm encountering a wierd bug on my I3 Solar (50mm). I have long press down set to enable DND but this happens with any of the hot key options.
If I activate the hot key, it will toggle DND but one of two things will happen when it's activated: either I (1) get no confirmation at all that it worked or (2) I will get a pop up saying "unable to reply to the message".
If I am on the watchface, I almost always get #1 when I activate the hot key. The easiest way to get #2, almost every time, is to activate the hot key from Controls or glances.
I'm currently running latest firmware (7.08)