There are many factors when the mist comes out. Differences in temperature, water level, humidity and air flow can all play a factor. Each unit may sometimes work a little differently. You may notice on different days the mist may be more pronounced. I have noticed that sometimes if the heat is on longer in my house because its colder outside the mist will look much stronger in the air. I guess the air is dryer so it is more obvious. Just know that it is working.
Hope that helps.
Sincerely,
The Smiley Daisy Team