Same problem with my brand new zte zmax pro from metro pcs then soon after that the touchscreen will not respond to multitouches like when I'm playing games or zooming in on google earth. Could be hardware or firmware I honestly don't know.
Hopefully they will change this in their next update. I already wrote them a review about the internal SD card option on their website so maybe they will hear us out and add the format SD card as internal storage. I can't believe they didn't especially on android marshmallow.