TWI and BLE on nRF52840 DK


I am interfacing nRF52840 DK with the MAX30101 sensor. I am able to execute all the TWI transactions necessary by using port 0 pin 27 as SCL and port 0 pin 26 as SDA. 

However when i use port 0 pin 14 as SCL and port 0 pin 13 as SDA I am not getting any output. I used ble_app_uart example and added TWI drivers. Are pins 14 and 13 assigned to something else in the ble_app_uart example? 

Changing pins is not an option, please tell me how I can go about working TWI on these pins. 

Thank you.