Reset pin low every 100ms

[Lokefar]

I have a problem with some of my boards (2 out of 3). Every ~100ms the reset pin goes down ~500mV. I have attached an image of this.

Neither of the two boards has a drop on the reset pin if the boards are in Low Boot. Also if a finger is placed near the WiFi connector the problem disappear. However it remains if it is the SigFox connector that is touched.

All boards have the newest firmware.

Any ideas what might be wrong?