This anomaly applies to Revision 2, build codes QDAA-C00.
Pin mapping is not functional for PSELRESET.
When mapping GPIOs to nRESET according to nRF52820 Product Specification, nRESET is not connected to the GPIO as configured in UICR.PSELRESET[n].PIN.
When configuring PIN in UICR.PSELRESET[n] registers, clear bit 5 to 0.