Did anybody noticed the unsoldered pins at each corner of the ADC? Why did they do that? It looks pretty risky, because they can bend easily and short together. One pin seems to be soldered onto the pad from R189 next to it, so I hope those pins are internally not connected.
Maybe the ADC being used is a different one than the board was designed for?
Does it really help to put a heatsink onto the front of an IC or transistor package or does it only fool the temperature measurement to make you thinking it helps?
The plastic material has clearly a much higher tehermal resistance than the metal plate at the back, so I don't think it really helps much, especially when it is mounted without much thermal contact like the one in the picture.