[Moto Z2 Force  Guides, News, & Discussion] neelchauhan:
Keep in mind that I am not a developer (well, of Android ROMs, I actively contribute code to non-Android projects).

One of the problems (as described on replies of the LineageOS thread is that the Sprint Z2 Force is the fact that the phone defaults to 3G data, and sometimes may not have data at all. The reason why this bug exists is because Sprint uses different LTE APNs for newer devices like the Z2 Force, but LineageOS maintains the older set of Sprint LTE APNs which are still necessary for devices like the Samsung Galaxy S5.

LineageOS maintainers for our device are aware of this bug and are fixing it for 16.0. I have backported these changes as a apns-conf.xml here as I don't want to wait for working LTE. I can confirm this works on LineageOS 15.1 with Sprint LTE.

I assume you are familiar with tools like adb and fastboot. I will not provide instructions on how to install adb or fastboot, there is already a thread on XDA for this.

The steps are as follows:

You first need the apns-conf.xml from here (personal MediaFire link, sorry if it's not AFH, it's still safe), the TWRP .img file for the Moto Z2 Force (you don't have to flash it) if you use Lineage Recovery, a USB-C cable, and a computer with adb/fastboot. Also, booting TWRP on the Z2 Force (which I have done) does not mean you have to replace Lineage Recovery. I still have Lineage Recovery on my phone even after doing these steps.

Then, you need to reset the connection settings. To do this, you need to go to Settings -> Network & Internet, click on the three vertical dots, and touch Reset Wi-Fi, mobile, & Bluetooth

Press on Reset Settings and enter your PIN if you were asked to. Keep in mind that this will wipe all your connectivity settings, including Wi-Fi and Bluetooth

Power down your phone

Power it up in bootloader mode by pressing Power and Volume Down at the same time an release when you get the green Android robot

If you use Lineage Recovery, run fastboot and type in

fastboot boot PATH_TO_TWRP

in a command prompt or terminal

Repace PATH_TO_TWRP with the filename and location of the TWRP .img file. You will only boot TWRP once, you don't have to flash it.

If you have already flashed TWRP, go directly to recovery mode.

When you are in TWRP, enter your passcode if required, and mount the system partition by selecting Mount, and then selecting System

After you have mounted the system partition, click the Back button on the bottom of the screen and run the following in a command prompt or terminal:

adb push PATH_TO_APNS_CONF /system/system/etc/apns-conf.xml

Replace PATH_TO_APNS_CONF with the path to your apns-conf.xml.

The reason why it is /system/system and not /system is because TWRP's /system is LineageOS's /, and /etc in LineageOS is a symlink to /system/etc, so TWRP sees it as recursive symlink (/system/etc is a symlink to /system/etc) which won't work

Press Reboot, and then System

Once you are in Lineage, unlock your phone and repeat steps 2-3

Reboot again (just to be safe), and you should have working LTE

UPDATE: If a LineageOS update overwrites your apns-conf.xml, follow these steps again. The November 14th update did for me, and I followed these steps again to get working LTE.

UPDATE 3/13/19: If you are using LineageOS 16.0, this tutorial is no longer necessary as Sprint support is taken into account in LOS 16.

Feel free to comment if this works for you, or if you have any suggestions.