Why is SWDIO/SWCLK shorted to GND on my board?

According to the Nordic DevZone there are mainly two potential issues leading to a short on one of the SWD signals:

• ESD issue, likely when connecting an SWD programmer to the SWD signals.
• Connecting an SWD programmer while the target board is not connected to supply voltage.

Please make sure proper ESD precautions are taken into account (ESD wrist-strap, ESD base/mat) as well as make sure to first connect the supply voltage and then the SWD programmer.