I am able to use the 4G LTE connection with the Connect app on my Android phone just fine. The version of my Connect app is 6.4.1 and the phone I am using is a Google Pixel XL running on the Google Project Fi network. Just trying to give you some of the specifics of what I am using the app on in order to let you know what my environment is.
Thanks for the post. I am on iPhone 7/ios10.2 and connect app version 6.4 (whatever is available on App Store). I always see Red dot when I am connected to LTE network on top where it shows your phone number.