No data connection on H930DS on the 3 network, UK after reflashing Stock pie - LG V30 Questions & Answers

I can't get the data connection to work at all, and it won't even connect to a 4g network even when the signal is strong. Mine is a H930DS (Joan?)
I just reinstalled the stock pie using "H93031a_00_OPEN_EU_OP_1105.zip", I installed in TWRP. I followed the instructions on the first page of this thread .....
I have tried various custom roms on this phone but this stock pie is one of the very few that even recognizes the sim card. I settled on stock pie inspite of the bloatware.
The problem happens when the rom is brand new, before ANYTHING is disabled or removed.
When I choose to search for a Network Operator (using the 3 Network sim) I get a "3 RAT-4G" and a "3 RAT-3G" listed and it will never connect to the 4G if I choose that one. It will only connect to the 3G. Even when the signal is very strong (5 bars). When I opt to connect to the 3G network then I get a stronger signal if I choose "GSM/WCDMA auto" in "settings>>network>>mobile netwroks>>network mode" but still no data connection
THESE DIDN'T HELP
1 - using ADB and restarting the phone in bootloader. It was to reset the modem I think. There was a series of 3 commands to follow. i can't remember the details of this method but I think one of the commands included "fastboot erase modemst2". I tried it and I was getting the same error message that other people reported and it didn't go anywhere.
2 - The following solution didn't work either..............
"re-loading IMS settings using the LG Hidden menu: Dial *#546368#*930# using the stock dialer -> Field Test -> IMS Setting -> Test -> Load Preset Configuration -> Initialize Configuration. Then back out twice to Field Test -> IMS Setting -> Test -> Restart IMS process. Give it a few minutes."
3 - Resetting network settings didn't help either (Settings -> General -> Reset -> Network settings reset).
4 - Changing APN, or network bands (in settings ... choosing "LTE/GSM/WCDMA auto" or "GSM/WCDMA auto" or "WCDMA only")
5 - Changing "set preffered network type" in engineering mode settings (accessing using *#*#4636#*#*)
How can I use data connection on my H930DS?

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Data modem works now!
SOLVED!
My phone has bootloader unlocked and TWRP revcovery. That's obvious I know but I only say it again in case anyone tries this with a locked bootloader and using a stock rom that has never been flashed. (I have to warn you that your results will be different, your rom will be reset for sure an your data will be wiped).
I tried so many things, flashing up and down from 8 to 10 but Stock Pie was always the least buggy for me so I persevered with that.
I think this solution reset the hardware, but I am no expert.
The solution is basically a "Factory Reset (R&D Only)". They warn you against it but with my configuration all it did was reboot the phone into recovery and then left it for me to decide what to flash or wipe, as per usual. What I only realized later, when I rebooted into system (without changing anything in TWrP) was that it had reset the hardware, or reactivate data connectivity. NowI have 3g data connection and 4g connection.
THE SOLUTION
*the following 4 lines are a direct quote (my phone's os DID NOT reset)
1) Backup everything, as the phone will be wiped. If yours is a network unlocked carrier model, make sure you have an unlock code (or unlock approval if T-Mobile).
2) Remove your Google account to disable Android Device Reset Protection.
3) Dial *#546368#*930# (replace 930 with your model number). This should open the service menu. From there SVC Menu - Factory Reset (R&D Only).
This takes quite a bit longer than normal Factory Reset. Your phone is now TRULY back to factory state.
I took out the sim and sd card before I committed to the reset. But like I said, it didn't wipe anything (maybe it would have wiped my sd card but I am not testing that). It just booted into recovery and when I rebooted into system I found that the data connection was working. Now finally it is a smartphone!