Here is how to get into the Hidden menu

[hanarachu]

I think you can get hidden menu through shorcut master app and you can enable lte bands from that for info How to enable 4G LTE on LG G3 to use Jio SIM | Digit Direct

 

[chalug]

Your method of accessing the "hidden menu" is correct. I used that to fix my issue. I also used a post on reddit from PetrasSukys to finish the task of fixing my proximity sensor AND IT WORKED! Yay!
Here are PetraSukys steps. I changed step 1 to use the code you provided:

1. Hidden menu code: ##228378
2. Device Test
3. MT [prompts for reboot]
4. [reboots into MiniOS (yes, it said like that)
5. Third item from the bottom "Individual Item(+power)". Activate by tapping while holding power button
6. 4th item from the bottom "Sensor Test" (not 4th from bottom for me, just search the menu for it)
7. Do what it says (repeatidly block sensor with hand, remove hand)
8. [returns to previous menu]
9. last item "Back to the MainList"
10. "Normal Boot(+power)" the same as step 5.

This worked for me. I hope it works for others!