LTE connection

Im having trouble in getting LTE mobile data at certain places . but 1months ago it all works just fine, now at certain time at that certain places LTE disconnected and keep searching for network. i had to change to 3g/2g to get data and making calls sms. i already changed the sim to another phone and it work just fine. contacted the carrier and they said no issues. please help. i havent hard reset the phone as the games takes too much time to download but if the solution is that then i have no choice