This occurrence was a year ago, but it kept bugging me until this day. I am a frequent flyer and this happened only this one time. While the plane (a Swiss A320) was still by the gate and the boarding just completed, the attendants asked the passengers to open the overhead vents because (not sure about the exact term) they have cooling difficulties. At that point it sounded reasonable, but it was around 09:00 in the morning and it wasn't a particularly warm day, it was 20°C at most outside (history says that the maximum temperature that day was 25°C). Roll-back and lift off were briefly after the boarding was complete.
Does a request like that indicate a failure or pressurization issue? I believe we were safe, just curious.