I just got an iPad Mini 4 with AT&T as the carrier yesterday. And for 24 hours now, all I get is ONE DOT of signal. It'll start out with 3 or 4, then after a couple of minutes, it's down to one. Sometimes it'll creep back up to two dots for a minute or so, and then it's back to one. With past AT&T iPads, I steadily get four, with the occasional five appearing now & again. And the letters "LTE" even disappear now for awhile & "4G" is displayed, instead. Did I get a defective unit?