i have Xperia z2 5.1.1 D6503 and i have 4g sim but i can get only 3g signal i have reset mi apn setings and turn on 4g mod... But i thinck its only nottification bar error (when i stress test net speed on 3g and 4g netvorg i get much more speed on 4g) but in notifbar it still says 3g.
