Nighthawk/AT&T/Disconnecting #MR7400

I have an MR7400 mobile router.  I have 2 laptops and one smart phone connected to it.  Service by AT&T, unlimited data (or so they say).  While using the hotspot (from multiple locations) i get a "no internet" pop up/message on my laptop.  Phone data quits working until I turn off wifi.  The router shows it is connected to 4 bars of 4G or better.  AT&T has replaced the router once already and now settled on "just deal with it"  .  Any thoughts?