ADuCM350 system clock issue

Hi,

we have built a PCB for impedance measurements with the ADuCM350 according to an Open-EIT project (https://github.com/OpenEIT). We currently try to make it run the impedance measurements with the given firmware, but the uC is running at 1MHz and doesn't change to the frequency of the external quarz chrystal of 16MHz. We try to figure out the reason for this.

Note: the pin VLCDVDD has not been connected to DVDD in the PCB design, which is - according to the data sheet - not critical to anything but the LCD- and GPIO-pins.

Does anyone have any recommendations for further issue analysis?

Best regards and thanks!