I am facing similar issue. found in this thread:
I used openOCD running on Raspberry Pi to debug nrf52480 dongle with Eclipse and but I experience some problems not being able to run my code on the dongle when pressing build in Eclipse. Nevertheless after removing the dongle from my Raspberry and plugging in again, the LED on dongle started to flash RED which looked ok again, but the openOCD offered me to enter command nrf52_recover. After this command the dongle stopped working. I probably erased the firmware which must be recovered. I am experiencing voltage 2.9V on C27,does that mean it could still be recovered? In this post the guy had 0V cross C27.If so, is it necessary to use J-link or any other probe to upload the firmware or is there any other way when having 2.9V across C27?