If you see a minus sign in the app instead of a bulb icon for one of your LIFX, please check the following:
- Is the light switch (power) on to allow the bulb to be turned off and on in the app?
- Is your home Wi-Fi network active and has internet access?
- Is the bulb correctly connected to the Cloud?
Power cycle the light.
If it does not reappear after about 60 seconds, try power cycling your router, then the bulb again, and wait another minute or so.