Some people reported improved LTE Connectivity by turning off connection optimizer. If after doing this you still see no improvements, then you are most likely in an area with towers that don’t support LTE or these LG phones are incompatible with some markets. The fix for the Verizon version is said to be a replacement Sim Card.
Sprint isn’t all that reliable in the twin cities area where it dissapointed me with constant dead spots. Good news is that Sprint said they will increase towers to make network more reliable.