I use smart lights myself. Incredibly useful and definitely takes the whole smart home up a notch. The most common issue I've faced with connectivity when I was setting them up was that they can only connect to the 2.4Ghz wireless frequency, so given that the Ignite modem (XB6/T) has band steering enabled they might be having difficulties identifying the appropriate frequency.
There's a couple of steps you can take though to assist in the connectivity process but given that you're unable to log into your Gateway though I would recommend contacting support so they can correct this issue.
Alternatively though you can:
Factory Reset your Ignite Modem - This will require a set up of your WiFi and a re-connection of your STB's.
This step can be skipped by contacting support.
Log into your Gateway and disable Band Steering temporarily.
Connect your smart lights to the 2.4Ghz wireless network
Re-enable band steering.
Your lights should remain connected.
These steps allow you to connected devices that may not "play well" with band steering, this this is admittedly rare it's possible this might be what you're experiencing.
If you do have any other questions though definitely let us know.
If you're not able to login using these instructions, please factory reset your modem by pressing in the small button labelled reset on the back and holding it for 10 seconds, then try again to login using the provided instructions.