Exact same thing happened to me yesterday with a boron. I re-flashed the latest bootloader and everything using the particle swd debugger, after which I was able to flash with boron cloud debug code, and now I just get:
deviceID=(removed but it was here and correct)
manufacturer=
model=
firmware version=
ordering code=
IMEI=
IMSI=
ICCID=
0000117150 [app] INFO: enabling trace logging
attempting to connect to the cellular network...
0000138303 [hal] ERROR: No response from NCP
0000138303 [hal] ERROR: No response from NCP
0000170553 [hal] ERROR: No response from NCP
0000170553 [hal] ERROR: No response from NCP
0000202803 [hal] ERROR: No response from NCP
0000202803 [hal] ERROR: No response from NCP
On a different (brand new) boron, I flashed tinker with 1.2.1-rc.1 and it connects to the cloud and then immediately starts blinking magenta and publishes spark/flash/status that it is updating (although I'm not sure why, it isn't part of any product) and reporting odd vitals like "-39kB of 32kB RAM used", and then eventually goes to safe mode and needs to be reflashed with an older deviceOS version to function again. The newer device remains recoverable, however I cant seem to get the old one going again. Unfortunately no suggestions, but you're not the only one!