I have a few Electrons that, on reset, will breath White then switch to flashing blue. This is on initial start up with 3rd party SIM card. I have no issues with 15 or 20 other devices. I am connected to USB and using a battery, connected to an external antenna.
My process when I receive a new Electron is; I put in 3rd party SIM and upload firmware downloaded during provisioning with the correct APN. Once the device has been connected and added to the Particle cloud I update to 0.5.3, then 0.6.0 and install my firmware.
However, a few devices I can never get connected, they just go from breathing white to flashing blue. I have updated them to 0.6.0, used different SIM cards, bent the SIM card pins up to be sure there is a good connection, reflashed firmware, reflashed with my product firmware, all without success.