There is a fast cyan blink which indicates cloud handshake, but I don’t know if this would qualify as “very fast” and usually (when happening over extended periodes) comes with the occassional orange/red burst, indicating the said keys issue.
For more keys issue remedies you could search for “red burst” or “orange burst” - even when intended for the Photon they might work for the Electron too.
e.g.
Photon setup flashing cyan with a "quick red burst" (now orange burst) [Solved]