If you change your router, and the SSID (network name) and password are different, you'll notice that your bulbs show as offline in the app.
There are two ways to troubleshoot this.
1. Rename your new Router SSID (network name) to your previous name, remembering that capitalization and spacing matters and use the exact same password.
All your lights should populate back in the app and be synced up to your new router.
2. If you would like to change the SSID, and password, you will have to reset your bulbs and set them up again.
www.lifx.com/setup can walk you through the process.
Note: Ensure that the 2.4ghz and 5ghz have different SSIDs and make sure you are connected to the 2.4ghz.