I’m having the same issue here, combined with a few others.
I have a custom board with a P1 that has worked fine in the past. Was able to connect to wifi, claim etc.
Butm I noticed it wasn’t working with our SoftAP setup web app like normal, so I decided to do a firmware upgrade, starting with just flashing tinker to trigger the latest one.
After particle flash --usb tinker the device went into constant blinking cyan. After some research I assigned new public keys. Twice. No dice.
Also manually upgraded firmware to the latest with .bin files in dfu mode. No dice there either (or with previous versions).
Not just trying to get into safe mode doesn’t even work. When I let go of the setup button it essentially resets and goes right back to blinking cyan.
Very stumped!