Default [Q] LTE/3G switch issue

Hi, I have an F340L and from the hidden menu I've set the Data connection to Global+LTE. When I'm in an LTE area the phone automatically connects to the 3G network and not to 4G. In order to make a 4G connection I have to enter the hidden menu, set it to LTE only, the device reboots and then the LTE connection is possible. Why is that? I mean why the device prefers 3G in an LTE area and needs the above procedure. Is there anyway to bypass that without a reboot or even automatic 4G connection? Any workaround, input or comments are welcome.