ITCC overheating in 2WD mode

[ml27]

I have installed the Syvces ECU and AWD controller in my GR Yaris, and I took it for Dyno tuning today. During the tuning process, I used the 2WD mode by applying the handbrake. However, after several ramp runs, the dash popped up the message of AWD system overheated and switched for 2WD mode. I checked the datalog for the temperature of the centre diff (ITCC) and found that it exceeded 100°C. As I switched it to 2WD by applying handbrake at the beginning and suppose the rear end was fully disengaged, why the ITCC would became overheat if the car was in 2WD mode. It sounds like the car was not in true 2WD mode or at least the ITCC was not fully disengaged to generate substantial heat.

Has anyone else experienced this or have any knowledge to explain if this is normal?

Thanks in advance.