LORA SUb-phy

I'm Developing a RF based communication between two LORA  developments kits of STM32,Part.no:b-l072Z-LRWAN-1.I  was using the USB stlink for a long time for debugging it.But suddenly the Built in STlink is not working.The Stlink LED(LD5) is toggling (While is stays high is a working board).Please Suggest me a possible way to solve the stlink issue or an alternate for the built in stlink to debug the Board.