My LG G3 D851 restart when i set sim network to gsm only

[AC Question]

i buy lg g3 mobile and after some days i noticed that when i go to area where no 3g or lte network then it set to gsm. Then mobile restart and it continuously restart untill a 3g or lte network was not found. at some forms i found it was battery problem so i buy a new battery but it does not help.
any help regarding this problem will be great for me.
thanks