RX pin no longer working on XIAO BLE

Hello all,
I have 3 Seeed XIAO BLE NRF52840 and I can no longer get the serial port working.
This has happened on the 3 boards.
I managed to isolate the problem by simply using P1_12 as input (or input pullup), but it is not able to detect any changes when pulled high or low.

To clarify, SerialUSB is still working. I am trying to communicate with another board hooked on pin 7.
Would anyone have any hints to get it working again?

Many thanks!