Arris sbg 10

I recently upgraded my device to a new modem/router unit. My initial attempts to activate the device resulted in "connected with no internet" and a tech visit was scheduled. Cables were checked to be "finger tight" and multiple restarts were done but the modem could not receive a signal. I returned the unit to the store as defective and got a replacement. 

The second unit was initially not receiving a signal but then I was able to connect to wifi but my devices kept requiring a sign in on an xfinity landing page saying I need to activate internet. 

I've noticed multiple people have had this issue with this device. Does anyone have a fix? I don't want to return another unit. Any ideas?