Thank you for the replies, greatly appreciated.
The images actually look OK. The "colder" images have less hot pixels and the hot pixels are also less bright. They also seems less noisy compared to the "warmer" images. The average deviation of the "colder" images is also smaller, indicating less noise. Nothing weird there I would say.
So it must be my way of calculating the dark current. I am still relatively new with PixInsight but the use of BasicCCDParameters script seems quite straightforward. I was following
this guide.