I managed to update keys on Photon Redboard under DFU mode. Redboard can be put in DFU mode successfully (blink yellow). However, I got "Error - No DFU device found" when executed 'particle keys server' or 'particle keys doctor' command. I also tried 'dfu-util -l' and got 'Cannot open DFU device 2b04:d008'.
dfu-util version is 0.8. And I've done the same thing on Photons for many time without any problem. Any clue or suggestion?