This can happen when a plane comes in and sits for hours and they don't put an external A/C hose on it. Once it heats up (only takes a short time) it can become dangerously hot, over 100 deg in the jet and it takes a while to cool down. If it's a 777 or 747, it can take quite a while.

Could have been a sensor on the plane, or a sensor on the A/C unit, no way of knowing. Not that it really mattered in the end, still a delay.

AD