I'm on 3 uk and was in the same situation - no LTE option.
Rang 3 technical support and they said that I'd have to take it up with LG, so no help there.
Tried a few things I found on here in terms of hidden menus, but nothing worked. So, found the LTECONFIGS app, and in the app settings menu, clicked 'uninstall updates'. Bingo. LTE option returned, and when I selected it, phone then picked up 4G signal.
Not sure if this is long term solution, but it works for now.