In hot setting, Dyson Purifier Hot + Cool will turn fan on 10 speed randomly

I use the Dyson purifier Hot + Cool in my bed. I’ve mostly loved it, but this issue has remained for months that I haven’t found a solution for yet. Overnight, I set the heat temperature to 21degrees C on a fan setting of 3. This is ideal since it often turns on nicely when the temperature drops and the lower fan setting ensures air is not blasting out. However, about once-a-week or so, at some point in the middle of the night, the purifier will switch to 10 setting and turn the heating off. So it’s just blasting cold air into our bedroom. I assume this is something that the air quality has reached an undesirable level and needs to stop heating to fix the air quality? This is uncomfortable for me, but since I still have a tiny baby sleeping in the same room, it has become more of a health/safety issue. How can I turn this function off and ensure the heat stays on at the temperature and fan setting that I set at the beginning of the night? All assistance is appreciated.